question

accuracy

answer

degree to which a measurement or an estimate based on measurements represents the true value of the attribute that is being measured

question

acute disease

answer

referring to a health effect, with sudden onset, often brief; sometimes loosely used to mean severe

question

acute disease

answer

referring to exposure, either brief, intense, or short-term; sometimes specifically referr ing to brief exposure of high intensity

question

adjusted rate

answer

rate in which the effects of differences in composition of the populations being compared have been minimized by statistical methods

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age-specific rate

answer

rate for a specified age group; numerator and denominator refer to the same age group

question

association

answer

(Syn: correlation, [statistical] dependence, relationship) Statistical dependence between two or more events, characteristics , or other variables. An association is present if the probability of occurrence of an event of characteristic , or the quantity of a variable, depends upon the occurrence of one or more other events, the presence of one or more other characteristics, or the quantity of one or more other variables

question

attributable risk

answer

rate (proportion) of a disease or other outcome in exposed individuals that can be attributed to the exposure. This measure is derived by subtracting the rate of the outcome (usually incidence or mortality) among the unexposed from the rate among the exposed individuals; it is assumed that causes other than the one under investigation have had equal effects on the exposed and unexposed groups

question

bias

answer

deviation of results or inferences from the truth, or processes leading to such deviation. Any trend in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth

question

case

answer

In epidemiology, a person in the population or study group identified as having the particular disease, health disorder, or condition under investigation

question

case-control study

answer

(Syn: case comparison study, case compeer study, case history study, case referent study, retros pective study) The observational epidemiologic study of persons with the disease (or other outcome variable) of interest and a suitable control (comparison, reference) group of persons without the disease

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case fatality rate

answer

proportion of cases of a specified condition which are fatal within a specified time

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cause (determinant)

answer

factor or event that is capable of bringing about change in health

question

chronic

answer

referring to a health-related state, lasting a long time. 2. Referring to exposure, prolonged or long-term, often with specific reference to low intensity. 3. The US National Center for Health Statistics defines a ' chronic' condition as one of 3 months' duration or longer.

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clinical

answer

concerned with or based on actual observation and treatment of disease in patients rather than experimentation or theory

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clinical trial

answer

(Syn: therapeutic trial) A research activity that involves the administration of a test regimen to humans to evaluate its efficacy and safety. The term is subject to wide variation in usage, from the first use in humans without any control treatment to a rigorously designed and executed experiment involving test and control treatments and randomization

question

Clinical Trial, Phase I

answer

trial Safety and pharmacologic profiles. The first introduction of a candidate vaccine or a drug into a human population to determine its safety and mode of action. In drug trials , this phase may Include studies of dose and route of administration. Phase I trials usually involve tewer than 100 healthy volunteers

question

Clinical Trial, Phase II

answer

pilot efficacy studies. Initial trial to examine efficacy usually in 200 to 500 volunteers; with vaccines, the focus is on immunogenicity, and with drugs , on demonstration of safety and efficacy in comparison to other existing regimens. Usually but not always, subjects are randomly allocated to study and control groups .

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Clinical Trial, Phase III

answer

intended for complete assessment of safety and efficacy. It involves larger numbers, perhaps thousands, of volunteers, usually with random allocation to study and control groups, and may be a multicenter trial

question

Clinical Trial, Phase IV

answer

trial With drugs, this phase is conducted after the national drug registration authority (e.g ., the Food and Drug Administration in the United States) has approved the drug for distribution or marketing. Phase IV trials may include research designed to explore a specific pharmacologic effect, to establish the incident of adverse reactions, or to determine the effects of long-term use. Ethical review is required for phase IV clinical trials , but not for routine post marketing surveillance.

question

cohort study

answer

(Syn: concurrent, follow-up, incidence, longitudinal, prospective study) The analytic method of epidemiologic study in which subsets of a defined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed In different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease or other outcome

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community

answer

group of individuals organized into a unity, or manifesting some unifying trait or common interest; loosely, the locality or catchment area population for which a service is provided, or more broadly, the station, nation, or body politic

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confidence interval

answer

computed interval with a given probability, e.g., 95%, that the true value of a variabl e such as a mean, proportion, or rate is contained within the interval.

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confounder (confounding)

answer

(From the Latin confundere, to mix together) 1. A situation in which the effects of two processes are not separated. The distortion of the apparent effect of an exposure on risk brought about by the association with other factors that can influence the outcome. 2. A relationship between the effects of two or more causal factors as observed in a set of data such that it is not logically possible to separate the contribution that any single causal factor has made to an effect. 3. A situation in which a measure of the effect of an exposure on risk is distorted because of the association of exposure with other factor(s) that influence the outcome under study.

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control group (or comparison group or controls )

answer

subjects with whom comparison is made in a case control study, randomized controlled trial , or other variety of epidemiologic study

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cross-sectional study

answer

(Syn: disease frequency survey, prevalence study) A study that examines the relationship between diseases (or other health-related characteristics ) and other variables of interest as they exist in defined population at one particular time.

question

crude rate

answer

summary rate based on the actual number of events In a population over a given time period.

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cumulative incidence (cumulative incidence rate)

answer

(Syn: incidence proportion) The number or proportion of a group of people who experience the onset of a health-related event during a specified time interval; this interval is generally the same for all members of the group, but, as In lifetime incidence, it may vary from person to person without reference to age.

question

death rate

answer

estimate of the portion of a population that dies during a specified period. The numerator is the number of person dying during the period; the denominator is the number in the population, usually estimated as the midyear population.

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descriptive epidemiology

answer

epidemiologic studies that are concerned with characterizing the amount and distribution of heath and disease within a population

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dose-response

answer

relationship of observed outcomes (responses) in a population to varying levels of a protective or harmful agent such as a form of medication or an environmental contaminant

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double-blind (masked) trial

answer

procedure of blind assignment to study and control groups and blind assessment of outcome, designed to ensure that ascertainment of outcome is not biased by knowledge of the group to which an individual was assigned. Double refers to both parties, i.e., the observer(s) in contact with the subjects and the subjects in the study and control groups

question

ecologic fallacy

answer

(Syn: aggregation bias , ecological bias) The bias that may occur because an association observed between variables on an aggregate level does not necessarily represent the association that exists at an individual level

question

ecologic study

answer

study in which the units of analysis are populations or groups of people, rather than individuals. An example is the study of association between median income and cancer mortality rates in administrative jurisdictions such as states and counties

question

effect modification (modifier)

answer

(Syn: conditional variable, moderator variable) A factor that modifies the effect of a putative causal factor under study. Effect modification is detected by varying the selected effect measure for the factor under study across levels of another factor

question

environment

answer

all that which is external to the Individual human host. Can be divided Into physical, biological, social, cultural, etc ., any or all of which can influence health status of populations

question

epidemiology

answer

study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems

question

etiologic fraction (attributable fraction, attributable risk percent)

answer

proportion of all cases that can be attributed to a particular exposure. It is the attributable difference (attributable risk ) divided by the incidence rate in the group. If the association is causal, this is also the proportion by which the incidence rate would be reduced if the exposure were eliminated. The attributable fraction may apply to exposed individuals (attributable risk percent) or to the whole population (population attributable risk percent).

question

etiology

answer

uterally, the science of causes, causality; in common usage, cause

question

experimental study

answer

study In which conditions are under the direct control of the investigator. In epidemiology, a study in which a population is selected for a planned trial of a regimen whose effects are measured by comparing the outcome of the regimen in the experimental group with the outcome of another regimen in a control group.

question

exposure

answer

Proximity and for contact with a source of a disease agent in such a manner that effective transmission of the agent or harmful effects of the agent may occur. 2. The amount of a factor to which a group or individual was exposed; sometimes contrasted with dose, the amount that enters or interacts with the organism. 3. Exposures may of course be beneficial rather than harmful, e.g., exposure to immunizing agents. 4. The process by which an agent comes into contact with a person or animal in such a way that the person or animal may develop the relevant outcome, such as a disease.

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external validity

answer

study is externally valid, or generalizable, if it can produce unbiased inferences regarding a target population (beyond the subjects in the study).

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false negative

answer

negative test result in a person who possesses the attribute for which the test is conducted.

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false positive

answer

positive test result in a person who does not possess the attribute for which the test is conducted

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follow-up period

answer

observation over a period of time of an individual, group, or initially defined population whose characteristics have been assessed in order to observe changes in health status or health related variables

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genetics

answer

branch of biology dealing with heredity and variation of individual members of a species

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Hawthorne effect

answer

effect (usually positive or beneficial) of being under study upon the persons being studied; thei r knowledge of the study often influences thei r behavior

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Health Insurance Portability and Accountability Act (HIPAA)

answer

federal act passed in 1996 that requi red the Department of Health and Human Services to publicize standards for the electronic exchange, privacy and security of health information

question

healthy worker effect

answer

phenomenon observed Initially in studies of occupational diseases. Workers usually exhibit lower overall death rates than the general population, because the severely ill and chronically disabled are ordinarily excluded from employment. Death rates in the general population may be inappropriate for comparison if this effect is not taken into account.

question

host

answer

epidemiologic context, the host may be the population or group; biological, social, and behavioral characteristics of this group that are relevant to heath are called "host factors."

question

human subjects

answer

individuals who consent to participate In a scientific Investigation

question

hypothesis

answer

supposition, arrived at from observation or reflection, that leads to refutable predictions. 2. Any conjecture cast in a form that will allow it to be tested and refuted.

question

incidence

answer

(Syn: incident number) The number of new events, e.g. , new cases of a disease in a defined population, within a specified period of time

question

incidence density (incidence rate)

answer

rate at which new events occur in a population. The numerator is the number of new events that occur in a defined period; the denominator Is the population at risk of experiencing the event during this period, sometimes expressed as persco-tlme.

question

index case

answer

first case in a family or other defined group to come to the attention of the investigator

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induction period

answer

period required ror a specific cause to produce disease. More precisely, the interval from the causal action of a factor to the initiation of the disease.

question

information bias

answer

(Syn: observational bias) flaw in measuring exposure or outcome data that results in a different Quality (accuracy) of information between comparison groups.

question

informed consent

answer

Voluntary consent given by a subject-Le., person or a responsible proxy (e.g., a parent)- for participation in a study, immunization program, treatment regimen, etc ., after being informed of the purpose, methods, procedures, benefits and risks, and, when relevant, the degree of uncertainty about outcome.

question

internal validity

answer

index and comparison groups are selected and compared in such a manner that the observed differences between them on the dependent variables under study may, apart from sampling error, be attributed only to the hypothesized effect under investigation

question

interviewee bias (or response bias)

answer

systematic error due to differences in characteristics between those who choose or volunteer to take part in a study and those who do not

question

latent period (latency)

answer

delay between exposure to a disease-causing agent and the appearance of manifestations of the disease.

question

lead time bias

answer

(Syn: zero time shift) Overestimation of survival time, due to the backward shift in the starting point for measuring survival that arises when diseases such as cancer are detected early, as by screening procedures.

question

length bias

answer

systematic error due to selection of disproportionate numbers of long-duration cases (cases who survive longest) in one group but not in another. This can occur when prevalent rather that incident cases are included in a case control study

question

matching

answer

process of making a study group and a comparison group comparable with respect to extraneous factors

question

measurement error

answer

mismatch between an estimated value and its true value. Can be observed when using multiple measures of the same entity or concept

question

misclassificatlon

answer

erroneous classification of an individual, a value, or an attribute into a category other than that to which it should be assigned. The probability of misclassification may be the same in all study groups (nondifferential misclassification) or may vary between groups (differential misclassification)

question

morbidity

answer

departure, subjective or objective, from a state of physiological or psychological well-being

question

mortality

answer

occurrence of deaths in a population

question

natality

answer

occurrence of births in a population

question

natural history of disease

answer

course of a disease from onset (inception) to resolution. Many diseases have certain well-defined stages that, taken all together, are referred to as the "natural history of the disease" in Question.

question

null hypothesis

answer

(Syn: test hypothesis) statistical hypothesis that one variable has no association with another variable or set of variables, or that two or more population distributions do not differ from one another.

question

observational study

answer

(Syn: nonexperimental observer bias:Systematic difference between a true value and that actually observed, due to failure of the observer to measure or identify the phenomenon accurately.

question

odds ratio

answer

(Syn: cross-product ratio, relative odds) ratio of two odds

question

period prevalence

answer

total number of persons known to have had the disease or attribute at any time during a specified period.

question

person-time (person-years)

answer

measurement combining persons and time as the denominator in incidence and mortality rates when, for varying periods, individual subjects are at risk of developing disease or dying.

question

personal identifiers

answer

information, including demographic data, that relates to the individual's past, present or future physical or mental health or condition, the provision of health care to the individual , or the past, present or future payment for the provision of health care to the individual

question

point prevalence

answer

number of persons with a disease or an attribute at a specified point in time.

question

population attributable risk

answer

(Syn: population risk difference) The incidence of a disease in a population that is associated with (attributable to) exposure to the risk factor. It is often expressed as a percentage (i.e., population attributable risk percent, population etiologic fraction).

question

population survey

answer

investigation in which information is systematically collected but in which the experimental method is not used.

question

precision

answer

quality of being sharply defined or stated. 2. In statistics, precision is defined as the inverse of the variance of a measurement or estimate.

question

predictive value (positive and negative)

answer

In screening and diagnostic tests, the probability that a person with a positive test is a true positive (l.e., does have the disease) is referred to as the ' predictive value of a positive test. " The predictive value of a negative test is the probability that a person with a negative test does not have the disease. The predictive value of a screening test is determined by the sensitivity and specificity of the test, and by the prevalence of the condition for which the test is used.

question

prevalence

answer

number of events, e.g., instances of a given disease or other condition, in a given population at a designated time.

question

primary prevention

answer

Activities, designed to reduce the occurrence of disease, that occur during the period of prepathogenesis, t.e., before an agent interacts with a host

question

probabilllty sample

answer

(Syn: random sample) All individuals have a known chance of selection. They may all have an equal chance of being selected, or, if a stratified sampling method is used, the rate at which individuals from several subsets are sampled can be varied so as to produce greater repres entation of some classes than of others

question

proportion

answer

type of ratio in which the numerator is included in the denominator

question

proportional mortality ratio

answer

proportion of observed deaths from a specified condition in a defined population, divided by the proportion of deaths expected from this condition in a standard population, expressed either on an age-specific basis or after age adjustment

question

P value (probability)

answer

probability that a test statistic would be as extreme as or more extreme than observed if the null hypothesis were true

question

quasi-experimental study

answer

situation in which the investigator lacks full control over the allocation andfor timing of intervention but nonetheless conducts the study as if it were an experiment, allocating subjects to groups. Inability to allocate subjects randomly is a common situation that may be best described as a qoeel-experlment

question

random error

answer

Fluctuations around a true value of a parameter because of sampling variability. Can occur as a result of poor precision, sampling error, or variability in measurement

question

randomization (randomized experiment)

answer

Allocation of individuals to groups, e.g., for experimental and control regimens, by chance

question

rate

answer

measure of frequency of occurrence of a phenomenon. In epidemiology, demography, and vital statistics, a rate is an expression of the frequency with which an event occurs in a defined population in a specified period of time

question

rate ratio

answer

ratio of two rates. The term is used in epidemiologic research with a precise meaning, i.e., the ratio of the rate in the exposed population to the rate in the unexposed population

question

ratio

answer

value obtained by dividing one Quantity by another: a general term of which rate, proportion, percentage, etc., are subsets. The important difference between a proportion and a ratio is that the numerator of a proportion is included in the population defined by the derominator, whereas this is not necessarily so for a ratio.

question

registry

answer

In epidemiology the term register is applied to the file of data concerning all cases of a particular disease or other health-relevant condition in a defined population such that the cases can be related to a population base

question

relative risk

answer

ratio of the risk of disease or death among the exposed to the risk among the unexposed

question

ratio of cumulative incidence rate

answer

in the exposed to the cumulative incidence rate to the unexposed, t.e., the rate ratio

question

rellabilillty

answer

degree of stability exhibited when a measurement is repeated under identical conditions

question

resistance

answer

ability of an agent to survive adverse environmental conditions

question

risk

answer

probability that an event will occur, e.g " that an individual will become ill or die within a stated period of time or by a certain age

question

risk difference

answer

(Syn: excess risk ) The absolute difference between two risks

question

risk factor

answer

AA aspect of personal behavior or life-style, an environmental exposure, or an inborn or inherited characteristic , that, on the basis of epidemiologic evidence, is known to be associated with health-related condition(s) considered important to prevent

question

risk ratio

answer

ratio of two risks, usually exposed/not exposed. sampling error (or sampling variation)

question

...

answer

that part of the total estimation error of a parameter caused by the random nature of the sample

question

screening

answer

defined in 1951 by the US Commission on Chronic Illness as, "the presumptive identification of unrecognized disease or defect by the application of tests, examinations or other procedures which can be applied rapidly. Screening tests sort out apparently well persons who probably have a disease from those who probably do not. A screening test is not intended to be diagnostic. Persons with positive or suspicious findings must be referred to their physicians for diagnosis and necessary treatment

question

secondary prevention

answer

intervention designed to reduce the progress of a disease after the agent interacts with the host; occurs during the period of pathogenesis

question

secular trends

answer

(Syn: temporal trend) Changes over a long period of time, generally years or decades. Examples include the decline of tuberculosis mortality and the rise, followed by a decline, In coronary heart disease mortality in many industrial countries in the past 50 years

question

sensitivity

answer

(of a screening test) proportion of truly diseased persons in the screened population who are identified as diseased by the screening test

question

specificity

answer

proportion of truly nondiseased persons who are so identified by the screening test

question

standardized mortality ratio

answer

ratio of the number of deaths observed in the study group or population to the number that would be expected if the study population had the same specific rates as the standard population, multiplied by 100. Usually expressed as a percentage

question

statistical significance

answer

statistical methods allow an estimate to be made of the probability of the observed or greater degree of association between Independent and dependent variables under the null hypothesis. From this estimate, in a sample of given size, the statistical ' significance" of a result can be stated. Usually the level of statistical significance is stated by the P value

question

stratification

answer

process of or result of separating a sample into several subsamples according to specified criteria, such as age groups, socioeconomic status, etc .

question

study population (sample)

answer

selected subset of a population

question

surveillance

answer

systematic ongoing collection, collation, and analysis of data and the timely dissemination of information to those who need to know so that action can be taken

question

target population

answer

collection of individuals, items, measurements , etc., about which inferences are desired . The term is sometimes

question

temporality

answer

timing of information about cause and effect

question

tertiary prevention

answer

an intervention, which takes place during late pathogenesis, designed to reduce the limitations of disability from disease

question

validity

answer

measurement - an expression of the degree to which a measurement measures what it purports to measure. Study the degree to which the inference drawn from a study, especially generalizations extending beyond the study population, are warranted when account is taken of the study methods, the representativeness of the study sample, and the nature of the population from which it is drawn

question

vital statistics

answer

systematically tabulated information concerning births, marriages, divorces, separations, and deaths based on registrations of these vital events

question

What is Epidemiology?

answer

Epidemiology is the study of the distribution and determinants of health and disease in populations. It is also the basic science underlying much of public health and preventive medicine.

question

Specifically what is epidemiology?

answer

More specifically, Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control health problems- John Last, A dictionary of Epidemiology, Oxford University Press, 2001

question

Broadly, what is epidemiology?

answer

Broadly, Epidemiology is the study of disease in populations

question

Objectives of Epidemiology: 1.Identify cause of disease and risk factors How is the disease transmitted?

answer

Reduce/eliminate risk factors Reduce morbidity and mortality

question

Objectives of Epidemiology: 2.Find out the extent of the disease in the community What is the burden of disease?

answer

Health Services Planning Training of providers Surveillance

question

Objectives of Epidemiology: 3. Look at the natural history of the disease What is the prognosis? Can you live with it? What is the survival?

answer

Develop interventions and treatments

question

Objectives of Epidemiology: 4. Evaluate interventions and treatments Do they work?

answer

Improve methods

question

Objectives of Epidemiology: 5. Provide input on Public Policy

answer

Improve Public Health

question

Epidemiology deals with populations, thus involving:

answer

Rates and Proportions Averages Heterogeneity within populations Dynamics- demography, environment, lifestyle

question

As other sciences, Epidemiology involves measurement, entailing the need for:

answer

Definition of the phenomena Spectrum of the disease Sources of data

question

Most epidemiological studies involve comparison, introducing consideration of:

answer

Standards of reference for baseline risk Equivalent measures of accuracy Adjustment for differences

question

Epidemiology is multidisciplinary, since it must consider:

answer

-Statistics -Interpretation - consistence, plausibility, coherence -Mechanisms - pathophysiology, psychosocial, economic, environmental -Policy impact, implications, ramifications, recommendations, and controversy

question

Endemic:

answer

Habitual presence of disease within a given geographic area

question

Epidemic:

answer

Occurrence in a community of a group of illnesses of similar nature in excess of what would normally be expected. Amount of disease depends on # susceptible (at risk) and # not susceptible by way of immunization, past disease or genetics (immune).

question

Pandemic:

answer

worldwide epidemic

question

Common source:

answer

group of persons exposed to common agent - Point-exposed over a brief period of time - Intermittent-exposed over a long period of time

question

Propagated:

answer

spreads gradually from person to person

question

Mixed epidemic:

answer

common source and from person to person

question

OUTBREAK INVESTIGATION STEPS

answer

Define the epidemic - Cases - Population at risk - Determine attack rate - = Number of people at risk who develop the disease/Number of people at risk - Primary case- the person who gets the disease from the source - Secondary case- the person who gets the disease from the primary case - Secondary attack rate = person to person spread - = Number of persons who got sick via the primary case/ Number of persons exposed to primary case 2. Look for the time -place interactions of cases, persons 3. Look for combinations of variables 4. Develop hypothesis 5. Recommend control measures

question

Rates

answer

How fast is the disease occurring in the population?

question

Proportion

answer

What fraction of the population is affected?

question

Incidence

answer

Measure of risk (new cases)

question

Prevalence

answer

Measure of the burden of disease in a community (new and pre-existing cases) - Point prevalence: at a specific point in time - Period prevalence: during a specific period of time

question

Morbidity

answer

the occurrence of disease in populations; the number of cases of a particular disease reported within a particular society and within a particular period of time

question

Mortality

answer

Proportion in a population that dies during a specified period

question

Case Fatality (CF) or Fatality Rate

answer

measures the severity of disease. It is the ratio of deaths within a designated population of people with a particular condition, over a certain period of time. An example of a fatality rate would be 9 deaths per 10,000 people at risk per year. This means that within a given year, out of 10,000 people formally diagnosed with a disease, 9 died.

question

Epidemiology and Disease Prevention: Primary prevention

answer

prevent the disease from occurring (e.g. immunization)

question

Epidemiology and Disease Prevention: Secondary prevention

answer

modify the severity of the extent of the disease (e.g. better access to emergency care)

question

Epidemiology and Disease Prevention: Tertiary prevention

answer

rehabilitation; measures to prevent reoccurrence of disease

question

What is Descriptive epidemiology?

answer

Descriptive epidemiology describes the health conditions and health-related characteristics of populations, typically in terms of person, place and time. This information serves as the foundation for studying populations. It provides essential contextual information with which to develop hypotheses, design studies and interpret results.

question

What is Surveillance?

answer

Surveillance is a type of descriptive epidemiology that monitors change over time.

question

Types of descriptive studies (Epidemiology)

answer

- Routine analyses of vital statistics( births, deaths), communicable disease reports, other notifiable events( outbreaks, induced abortions) - Periodic surveys of health status, knowledge, belief, attitudes, practices, behavior, environmental exposures, and health care encounters (e.g. CDC) - Specialized surveys to establish prevalence of a condition, a characteristic or use of a medical procedure - Studies comparing information to look for differences and patterns. For example across migrants and persons in their country of origin.

question

What is Analytic Epidemiology?

answer

Analytic epidemiology involves the systematic evaluation of suspected relationships, for example between an exposure and a health outcome. These studies have a narrower focus and typically provide stronger evidence concerning particular relationships. These studies usually involve the testing of hypotheses.

question

Types of analytic studies (Observational and Experimental)

answer

- Case-control studies; comparison of people who develop a condition with people who do not - Follow up studies (retrospective, prospective): a comparison of people with and without a characteristic in relation to a health related event - Intervention trials (clinical, community); comparison of a subsequent experience exhibited by people to whom a treatment or preventative intervention has been given, to that of people not provided that intervention

question

Examples of Aggregate Data

answer

Vital statistics Data from government databases Summaries of disease and injury reporting systems and registries Environmental monitoring systems e.g. measures of air pollution Production and sales data

question

Examples of Individual Level data

answer

Vital events registration Disease and injury reporting systems and registries National Surveys Medical records Questionnaires Biological specimens

question

What is the most quantifiable error?

answer

The most quantifiable error is sampling error, which is the distortion that can occur from the 'luck of the draw'

question

Sampling errors

answer

Type I error and Type II error We make a correct decision if we: -Reject the null hypothesis when it is false -Do not reject the null hypothesis when it is true We make errors when we: - Reject the null hypothesis when it is true ( Type I error =a) - Do not reject the null hypothesis when it is false( Type II error =ß) Power = probability of detecting a difference if one truly exists, i.e. probability that a study will find a statistically significant difference, when a difference of a given magnitude truly exists. Power = 1- ß, where beta is the probability of declaring a difference not statistically significant, when a difference truly exists.

question

Selection bias:

answer

These are biases that result from the way study participants are selected from the source population. This error results when the sample/study participants is/are not representative of the population of interest. Causes of selection bias are -Self selection (volunteering) -Non response( refusal) -Loss to follow up (attrition, migration) -Choice of an inappropriate comparison group (investigator selection)

question

Control of selection bias:

answer

This can be controlled in the analysis by identifying factors which are related to subject selection and controlling for them as confounders (provided that these factors are not affected by study exposure or disease)

question

Minimizing selection bias:

answer

If selection bias has occurred in the enumeration of the exposed group, it may be minimized by choosing an appropriate no-exposed comparison group.

question

Information Bias:

answer

This is a systematic error due to incorrect definition, measurement or classification of variables of interest. This is bias that results from the misclassification of the study participants with respect to disease or exposure status .Two types of misclassification exist: Non- differential and differential. Non differential occurs when the probability of misclassification of exposure is the same for cases and non-cases. Differential misclassification occurs when the probability of misclassification of exposure is different in diseased and non-diseased persons. Sources of information bias are: - Errors in assignment of cause of death - Errors and omissions in medical records - False positives or negatives on diagnostic tests

question

Minimization of information bias:

answer

Ensure that the misclassification is non differential by ensuring that exposure information is collected in an identical manner in cases and non-cases.

question

Study Design Options

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All epidemiologic studies are based on a particular source population/ study population /base population, followed over a particular risk period. Within this framework a fundamental distinction is made between studies of disease incidence [number of new cases of disease over time], and studies of disease prevalence [number of people with the disease at a particular point in time].

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Incidence studies

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The Key feature of incidence studies is that they involve an event ( e.g. developing a disease for the first time) which occurs at a particular point in time, rather than a state (e.g. having a disease) which can exist over an extended period of time.

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Measures of disease occurrence in incidence studies: Incidence rate (hazard rate/force of mortality/incidence density):

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This is a measure of disease occurrence per unit population time, and has the reciprocal of time as its dimension . Rate ratio(incidence density ratio) is the ratio of the incidence rate in the exposed group to that in the non-exposed group

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Measures of disease occurrence in incidence studies: Incidence proportion (cumulative risk/average risk):

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This is the proportion of people who experience the outcome of interest at any time during the follow up period. Risk ratio (incidence proportion ratio or cumulative incidence ratio) is the ratio of the incidence proportion in the exposed group to that in the non-exposed group

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Measures of disease occurrence in incidence studies: Incidence odds:

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This is the ratio of people who experience the outcome to the ratio of people who do not experience the outcome. Odds ratio is the ratio of incidence odds in the exposed group to that in the non-exposed group.

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prevalence studies

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Prevalence : This denotes the number of cases of disease under study existing in the source population at a particular time. These studies are important as the enable assessment of the level of morbidity and the population disease burden for a non fatal condition.

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Point prevalence

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Point prevalence; estimated at one point in time . Period prevalence; denotes the number of cases that existed during some time interval.

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What kind of study should be used: When populations' exposure is not dichotomous, or when variations exist within the dichotomy

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- Cross sectional studies - Longitudinal studies: i) General, ii) Time Series

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What kind of study should be used: When level of measurement of exposure varies- complex study designs involving measurements of groups within populations, individuals, or both.

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- Ecologic studies - Multilevel studies

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Name three types of OBSERVATIONAL STUDIES:

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1.Cohort Studies 2. Case Control Studies 3. Cross Sectional Studies/Prevalence Studies

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Measurement of exposure and Health Status: Exposure:

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Any factor that is under study, or the presence of a factor in the external environment. Exposure levels can be assessed with regard to the (i) intensity of the substance in the environment and the (ii) duration of time for which exposure occurs.

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Measurement of exposure and Health Status: Dose:

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The amount of substance that reaches susceptible targets within the body. Methods of exposure measurement include personal interviews, questionnaires, diaries, observation, and routine records, and physical or chemical measurements on the environment or person. A Combination of the above is generally used. Recently biomarkers have been introduced to measure internal doses.

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Cohort Studies

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group of subjects who have shared a particular experience during a particular time span. The objective of a cohort study is to determine if the incidence of an event is related to a suspected exposure. Basic effect measures in a cohort study are the rate ratio and the risk ratio.

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Relative risk

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Relative risk = ratio of risk in the exposed to that in the unexposed.

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Cohort examples

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Community Occupational cohort Defined group Convenience cohort

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Exposure examples

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Medication Occupational exposures Habits Activities

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Outcome examples

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Cancer or other disease Death Recurrence, recovery

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Types of Cohort Studies:

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(A) Concurrent; (B) Non-concurrent

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Examples of (A) Concurrent/ Prospective / Longitudinal Study

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- Start now and follow into the future - Baseline exam, methods, follow up can be planned - Quality Control measures can be implemented - Disadvantages: Time and Cost

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Examples of (B) Non-concurrent /Historical /Retrospective

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- Cohort assembled in past, based on existing records - Follow up usually to current time for outcome - Useful in occupational studies - Advantage: Less expensive and less time consuming than concurrent - Disadvantage: existing records may have been limited or biased. Follow up may be difficult

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Case Control Studies

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Case-control studies compare the odds of past exposures to an agent/factor between cases (diseased) and controls (non-diseased). The standard effect estimate /estimate of relative risk in a case control study is the odds ratio (OR)

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Types of Case Control Studies

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(A) Case -Based Studies, (B) Nested Case Control Studies

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Characteristics of (A) Case - Based Studies

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- All cases occurring at some point in time (you may use incident or prevalent cases as described above) - Control selection can be difficult

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Characteristics of (B) Nested Case- Control Studies

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- Also called Case-Cohort Study: A case control study nested in a cohort study - Controls selected either at base line (case-cohort) or at the time the case occurs (nested) - Advantage - Data on exposure are obtained before disease develops - Possibility of recall bias is thus eliminated. - Less expensive than expanding the analysis to include the entire cohort - Here the OR is a statistically unbiased estimate of relative risk

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MATCHING

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Matching is used to make cases and controls as similar as possible with regard to potential confounding factors. For example matching on race, age, follow up time, etc

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Types of Matching:

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- Individual (pair): (one or more) control individually matched to a case from an eligible pool - Frequency matching: a group of controls so the distribution of characteristics in the cases and controls is similar - Minimum Euclidean Distance Measure: match closest eligible person to the case (" minimal space")

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Advantages of Matching:

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- May be the only way to control confounding ( where adjustment is difficult) - When limited to strong confounders, matching increases statistical power (efficiency) of the study - It is a straightforward way to obtain a comparable control group.

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Disadvantages of Matching:

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The association between the matching variable and outcome cannot be assessed. Therefore additive interaction cannot be assessed between matched variables and the exposure of interest - Requires the use of special analytic techniques - Overmatching- if matching variable is strongly correlated with the variable of interest- may eliminate ability to see a real association - If match variables are weak confounders, no statistical power is gained - Matching is Irreversible - Residual confounding occurs if you match continuous variables by category

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Cross Sectional Studies/Prevalence Studies

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This is a snapshot of a cohort regarding information on disease and exposure at a single point in time . These studies tell us the Prevalence and the Association.It is often the baseline information in a prospective cohort or longitudinal study. The issue of Temporality arises: Disease and exposure are "associated" however causation can not be implied if timing is unknown.

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randomized clinical trial

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A randomized clinical trial is an experiment use to test the efficacy or effectiveness of healthcare services. It involves the random allocation of participants to different treatments. Using chance to assign people to groups ensures that the groups should be similar and that the treatments they receive can be compared objectively. A field trial is a test of the performance of some new product under the conditions in which it will be used.

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Community intervention:

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intervention on a community wide basis e.g. fluoridation

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Cluster randomized trials

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Prevention/Field trials to groups rather than individuals

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Case -Cross Over Design

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- Cases serve as their own control - Value for some variable assessed or collected at the time of case determination is compared to value of variable at some previous time - Assumptions are that the (i)exposure effects are not cumulative, (ii)the disease has no pre-clinical stage that could affect exposure - Issue: Potential for recall bias.

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Characteristics of Randomized Clinical Trials (studies of specific drugs) and Field Trials (prevention strategies)

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- Random Assignment (to achieve baseline similarity),i.e. the comparison of treatment groups - Blinding (single , double , triple) - Placebo; equivalence, i.e standard treatment vs. - New prescriptions - Gold Standard for evidence, i.e the chance for bias is much less

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STUDY DESIGN ISSUES

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Reliability (precision) - reproducibility Validity (accuracy) - the absence of bias

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Precision (Reliability)-reproducibility

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Random error (lack of precision) will occur in any epidemiologic study. Increasing sample size, so that the precision of the effect estimate will be increased, would be the most effective way of reducing random error. It is important to, at the beginning of the study to determine a sample size that would be large enough to be informative. While the ideal study would be infinitely large, cost and number of available participants, create barriers to the sample size.

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Validity (Accuracy) - absence of bias

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Systematic error (lack of validity/bias), occurs if there is a systematic difference between what the study is actually estimating and what it is intended to estimate. Systematic error is distinguished from random error in that increasing the sample size does not reduce the chance of error.

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Quality Assurance :

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Activities to ensure quality of the data before data collection.

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Quality Control :

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Efforts to monitor and maintain the quality of data during the conduct of the study

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Confounding:

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A situation in which a non-causal association between a given exposure and an outcome is observed as the result of a third variable (or group of variables) OR distortion of an apparent effect of an exposure on risk brought about by the association with other factors that can influence the outcome. Confounding may result in an apparent strengthening, weakening, or elimination of a true causal association.

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A confounding variable must be

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- Related to both the exposure and outcome under study - Not an intermediate variable in the relationship ( except when exploring mechanisms)

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Types of confounding

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- Positive- When the crude RR /OR is further from 1.0 than the adjusted ratio - Negative-- When the crude RR /OR is closer to 1.0 than the adjusted ratio - Qualitative-when moving from an RR/OR that is at either side of 1.0

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Verification of presence of confounding

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- The potential confounding variable is related to both the exposure and the disease - The OR's in strata formed by the potential confounder are different from the crude OR's (pooled) - The crude measure of association (i.e. OR) differs from the measure adjusted for the potential confounder

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Control of confounding Prior to Data collection : Control in the study design

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- Random collection - Individual matching - Frequency matching

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Control of confounding After Data collection : Control in the Analysis

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- Direct adjustment - Indirect adjustment - Mantel-Haenszel - Regression Techniques

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INTERACTION

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This occurs when the incidence of disease in the presence of two or more risk factors differs from the incidence expected to result from their individual effects. In other words, - observed joint effects are more or less than expected joint effects - two or more factors modify the effect of each other with respect to disease - association is not equally strong across strata formed by the third variable

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Types of interaction: Synergistic or Positive-

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if the presence of the effect modifier accentuates the effect of the exposure of interest (categorical) or the outcome differs depending on the level of the effect modifier (continuous)

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Types of interaction: Antagonistic or Negative-

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if the presence of the effect modifier accentuates the effect of the exposure of interest (categorical) or the outcome differs depending on the level of the effect modifier (continuous)

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Types of interaction: Quantitative-

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interaction in the same direction from the crude RR/OR by stratum specific analysis, but the association still varying from stratum to stratum

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Types of interaction: Qualitative-

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interaction in the opposite direction (cross-over) from the crude RR/OR by stratum specific analysis, but the association still varying from stratum to stratum

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Temporality:

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The cause must precede the effect

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Specificity:

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Specificity of the effect is important in assessing possibility of biases

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Consistency:

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This is demonstrated by several studies giving similar results. Statistically it corresponds to homogeneity across studies

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When does a dose response relationship occur?

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A dose response relationship occurs when changes in the level of exposure are associated with changes in the prevalence or incidence of the effect that one would expect from biologic considerations. The absence of an expected dose -response relationship provides evidence against a causal relationship, while it s presence narrows the scope of biases that could explain the relationship.

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Stages in the Data Analysis:

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1. Hypothesis stage 2. Data Set Development Stage 3. Analysis Stage 4. Results and Conclusion Stage

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DATA ANALYSIS: HYPOTHESIS STAGE: Hypothesis Development

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- Define General hypothesis - Define Outcome variable - Define exposure or risk factor variable (s) - Recognition of study design needed to test hypothesis - Define specific hypothesis to be tested - If working from an existing data set can the hypothesis be tested adequately?

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DATA ANALYSIS: DATA SET DEVELOPMENT STAGE

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Data set description and formation of analytical data set - Verify data in data set - Compare your total count against documentation - And for key variables - Examine variables - Look for missing values - Look for unusual missing value codes e.g. 8888 - Look for implausible values - Formation of analytic data set: - Eliminate prevalent cases in analysis of cohort study data - Eliminate persons with missing data - Eliminate persons in specialized categories of analysis where the sample size is too small to produce informative results - Depending on specific hypothesis, other persons may need to be deleted, e/g age range

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DATA ANALYSIS: ANALYSIS STAGE

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- Develop an analysis strategy, e.g. the statistical model to be used - Estimate the maximum number of variables to be included in any model - Select a model building strategy for assessing interaction (effect modification), and confounding - Conduct analyses

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DATA ANALYSIS: RESULTS AND CONCLUSIONS

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- Examination results - Interpretation of results - Results evaluation: Do they make sense? - Limitations of study and analysis - Conclusion - Future analyses

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What would be the best source of information on adult and infant mortality? (A) Disease registers (B) Vital statistics (C) Special survey study (D) Hospital clinic statistics

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What would be the best source of information on adult and infant mortality? (B) Vital statistics Data are routinely collected on all deaths that occur in the US through death certificates. Death certificates record the age at death, and are reported through the vital statistics registration system. References: Friis and Sellers; pp. 190-191 | Last et al.; p. 187

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Which of the following terms is expressed as a ratio (as distinguished from a proportion)? (A) Male Births / Male + Female Births (B) Female Births / Male + Female Births (C) Male Births / Female Births (D) Stillbirths / Male + Female Births

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Which of the following terms is expressed as a ratio (as distinguished from a proportion)? (C) Male Births / Female Births A ratio is defined as "the value obtained by dividing one quantity by another; a general term of which rate, proportion, percentage, etc. are subsets." References: Last et al.; p. 152 | Friis and Sellers; p. 89

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Mortality rates by sex in the United States generally show the following sex differences: (A) Males greater than females (B) Females greater than males (C) Males equal to females (D) Males equal to females in the first years of life

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Mortality rates by sex in the United States generally show the following sex differences: (A) Males greater than females Males generally have higher all-cause age-specific mortality rates than femalesfrom birth to age 85 and older; in 2003, the ratio of male to female age-specific deaths was 1.4 to 1. References: Hebel and McCarter; p. 20 | Friis and Sellers; pp. 134-138

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Morbidity rates by sex in the United States show the following sex differences: (A) Males greater than females (B) Females greater than males (C) Males equal to females (D) Males equal to females in the first years of life

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Morbidity rates by sex in the United States show the following sex differences: (B) Females greater than males This is known as the female paradox: females have lower mortality but higher morbidity rates for acute and chronic conditions. Reference: Friis and Sellers; p. 136

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Case-control studies are among the best observational designs to study diseases of: (A) High prevalence (B) High validity (C) Low case fatality (D) Low prevalence

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Case-control studies are among the best observational designs to study diseases of: (D) Low prevalence The case control design is desirable when disease occurrence is rare, becasue if a cohort study were used in such a circumstance, a very large number of people would have to be followed to generate enoigh people with the disease for study. References: Hebel and McCarter; pp. 106-107, 118 | Friis and Sellers; pp. 243-247 | Kleinbaum et al.; pp. 31-32

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A valid conclusion derived from the above data concerning mortality among estrogen users is: (A) The mortality rates for cancer of the uterus are higher in estrogen users than non-users in both age groups studied A causal relationship cannot be demonstrated based on the results of a single study; the mortality rate is higher in users for both age groups. References: Friis and Sellers; pp. 110-112, 132-134 | Hebel and McCarter; pp. 17-22 | Kleinbaum et al.; pp. 64-66

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Comparison of mortality rates due to cancer of the uterus in users and non-users of supplemental estrogen revealed the following mortality rates per 100,000: A valid conclusion derived from the chart concerning mortality among estrogen users is: (A) The mortality rates for cancer of the uterus are higher in estrogen users than non-users in both age groups studied (B) A causal relationship is demonstrated between the use of estrogen and incidence of uterine cancer (C) Mortality from cancer of the uterus rises with age regardless of whether estrogen is used (D) The mortality rate is lower in non-users than users because the symptoms of uterine cancer are detected earlier in the former group of women

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In a large case-control study of pancreatic cancer, 20% of the cases were found to be diabetic at the time of diagnosis, compared to 5% of a control group (matched by age, sex, ethnic group, and several other characteristics) that was examined for diabetes at the same time that the cases were diagnosed. The authors concluded that diabetes played a causal role in the development of pancreatic cancer. This conclusion: (A) Is correct (B) May be incorrect because there is no control or comparison group (C) May be incorrect because of failure to establish the time sequence between the onset of diabetes and pancreatic cancer (D) May be incorrect because of less complete ascertainment of diabetes in pancreatic cancer cases (E) May be incorrect because of more complete ascertainment of pancreatic cancer in non-diabetic people

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In a large case-control study of pancreatic cancer, 20% of the cases were found to be diabetic at the time of diagnosis, compared to 5% of a control group (matched by age, sex, ethnic group, and several other characteristics) that was examined for diabetes at the same time that the cases were diagnosed. The authors concluded that diabetes played a causal role in the development of pancreatic cancer. This conclusion: (C) May be incorrect because of failure to establish the time sequence between the onset of diabetes and pancreatic cancer Case control studies cannot demonstrate the temporal relationship between an exposure and a disease. This is a requirement for concluding causality. References: Kleinbaum et al.; pp. 22-24 | Hebel and McCarter; pp. 140-141 | Friis and Sellers; p. 72

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Cohort study is to risk ratio as: (A) Ecologic fallacy is to cross-sectional study (B) Case-control study is to odds ratio (C) Genetics is to environment (D) Rate ratio is to ecologic study

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Cohort study is to risk ratio as: (B) Case-control study is to odds ratio The risk ratio is the measure of association for a cohort study; the odds ratio is the meausre of association for a case-control study. References: Kleinbaum et al.; pp. 74-75 | Friis and Sellers; pp. 240-241 | Last et al.; p. 128; Hebel and McCarter; p. 111

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It is essential in cohort studies of the role of a suspected factor in the etiology of a disease that: (A) There are equal numbers of people in both study groups. (B) At the beginning of the study, those with the disease and those without the disease have equal risks of having the factor. (C) The exposed and non-exposed groups under study should be as similar as possible with regard to possible confounders. (D) The incidence of the disease is low.

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It is essential in cohort studies of the role of a suspected factor in the etiology of a disease that: (C) The exposed and non-exposed groups under study should be as similar as possible with regard to possible confounders. This helps ensure comparability of the two groups, increasing the inetrnal validity of the findings. All other answers are false. Reference: Friis and Sellers; pp. 266-267

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A researcher is interested in identifying potential risk factors for a rare form of bone cancer in children. Which of the following study designs would be best suited to investigate the risk factors for this type of cancer? (A) Prevalence-survey (B) Case-control (C) Cohort (D) Descriptive (E) Experimental

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A researcher is interested in identifying potential risk factors for a rare form of bone cancer in children. Which of the following study designs would be best suited to investigate the risk factors for this type of cancer? (B) Case-control Case-control studies are best suited for rare diseases. References: Hebel and McCarter; pp. 106-107, 118 | Friis and Sellers; pp. 243-247 | Kleinbaum et al.; pp. 31-32

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Which of the following statements regarding disease measures is inaccurate? (A) Prevalence equals duration time incidence (B) Prevalence is a proportion (C) Cumulative incidence is a proportion (D) Incidence density is a proportion

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Which of the following statements regarding disease measures is inaccurate? (D) Incidence density is a proportion The numerator for incidence density is "number of cases" and the denominator is "person-time." This represents a rate and not a proportion. References: Last et al.; p. 92 | Hebel and McCarter; p. 25 | Friis and Sellers; p. 98 | Kleinbaum et al.; pp. 53-54

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In a population of 5,000 people, 100 ate spinach contaminated with E. coli (O157:H7) and became ill. Of the ill, 15 died. What was the case fatality rate? (A) 20 per 1,000 (B) 3 per 1,000 (C) 150 per 1,000 (D) 15 deaths

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In a population of 5,000 people, 100 ate spinach contaminated with E. coli (O157:H7) and became ill. Of the ill, 15 died. What was the case fatality rate? (C) 150 per 1,000 The numerator for case fatality is "number of individuals dying during a specified period of time from the disease of interest" and the denominator is "number of persons with the disease of interest." In this question, the numerator is 15 and the denominator is 100. 15/100 = 0.15 X 1000 = 150/1000 persons. References: Friis and Sellers; pp. 414-415 | Last et al.; p. 24 | Hebel and McCarter; p. 20 | Kleinbaum et al.; p. 63

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A case-control study comparing ovarian cancer cases with community controls found an odds ratio of 2.0 in relation to exposure to radiation. Which is the correct interpretation of the measure of association? (A) Women exposed to radiation had 2.0 times the risk of ovarian cancer when compared to women not exposed to radiation (B) Women exposed to radiation had 2.0 times the risk of ovarian cancer when compared to women without ovarian cancer (C) Ovarian cancer cases had 2.0 times the odds of exposure to radiation when compared to controls (D) Ovarian cancer cases had 2.0 times the odds of exposure to radiation when compared to women with other cancers

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A case-control study comparing ovarian cancer cases with community controls found an odds ratio of 2.0 in relation to exposure to radiation. Which is the correct interpretation of the measure of association? (C) Ovarian cancer cases had 2.0 times the odds of exposure to radiation when compared to controls. In a case control study, we are comparing the prevalence of exposure given disease status, therefore, we compare the prevalence of radiation among those with cancer to the prevalence of radiation among those without cancer. We cannot use "risk" to describe this association because risk implies probability and we are calculating odds. References: Friis and Sellers; pp. 240-241 | Last et al.; p. 128 | Kleinbaum et al.; pp. 74-75

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Double-blinded (masked) studies are an important way to: (A) Achieve comparability of cases and controls (B) Avoid observer and interviewee bias (C) Avoid observer bias and sampling variation (D) Reduce the effects of sampling variation (E) Avoid interviewee bias and sampling variation

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Double-blinded (masked) studies are an important way to: (B) Avoid observer and interviewee bias Double masking or blinding a study means that neither the patient nor the individuals involved in evaluating the outcome know the exact exposure status of any individual. This decreases the risk of observer bias because the observer does not know the true exposure. It also decreases the risk of interviewee bias because the participant doesn't know which exposure group he/she is in. References: Friis and Sellers; pp. 304-305 | Last et al.; p. 18 | Kleinbaum et al.; p. 26 | Hebel and McCarter; p. 125

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The difference between primary and secondary prevention of disease is: (A) Primary prevention focuses on control of causal factors, while secondary prevention focuses on control of symptoms (B) Primary prevention focuses on control of acute disease, while secondary prevention focuses on control of chronic disease (C) Primary prevention focuses on control of causal factors, while secondary prevention focuses on early detection and treatment of disease (D) Primary prevention focuses on increasing resistance to disease, while secondary prevention focuses on decreasing exposure to disease

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The difference between primary and secondary prevention of disease is: (C) Primary prevention focuses on control of causal factors, while secondary prevention focuses on early detection and treatment of disease Primary prevention suggest that the "incidence" of disease is prevented. In general, this means that the prevention has decreased the prevalence of risk factors or increased the prevalence of preventive factors thus changing the incidence of disease. In secondary prevention, disease has already occurred and the prevention program is designed to identify disease early so that treatment can be started early. References: Friis and Sellers; p. 80 | Last et al.; pp. 141-142 | Hebel and McCarter; p. 59

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A screening test is used in the same way in two similar populations, but the proportion of false-positive results among those who test positive in population B is higher than that among those who test positive in population A. What is the most likely explanation for this finding? (A) The specificity of the test is higher in population A (B) The specificity of the test is lower in population A (C) The prevalence of disease is higher in population A (D) The prevalence of disease is lower in population A

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A screening test is used in the same way in two similar populations, but the proportion of false-positive results among those who test positive in population B is higher than that among those who test positive in population A. What is the most likely explanation for this finding? (C) The prevalence of disease is higher in population A The number of false positives increases as the prevalence of the outcome of interest decreases. Communities with lower prevalence of outcome will have higher false-positive rates. I community B has higher false- positive rates, then it must have lower prevalence compared to population A. Therefore, population A has a higher prevalence of disease than community B. References: Friis and Sellers; pp. 382-385 | Hebel and McCarter; pp. 62-63 | Kleinbaum et al.; pp. 152-154 | Last et al.; p. 140

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The relative risk of dying for smokers compared to non-smokers is: {The death rate per 100,000 for lung cancer is 7 among non-smokers and 71 among smokers. The death rate per 100,000 for coronary thrombosis is 422 among non-smokers and 599 among smokers. The prevalence of smoking in the population is 55%.} (A) 9.1 for lung cancer and 0.30 for coronary thrombosis (B) 9.1 for lung cancer and 1.4 for coronary thrombosis (C) 10.1 for lung cancer and 8.4 for coronary thrombosis (D) 10.1 for lung cancer and 1.4 for coronary thrombosis (E) 12.4 for lung cancer and 1.7 for coronary thrombosis

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The relative risk of dying for smokers compared to non-smokers is: (D) 10.1 for lung cancer and 1.4 for coronary thrombosis Prevalence is not relevant to this question - so ignore the prevalence of smoking statement. The relative risk of dying from lung cancer for smokers compared to non-smokers is 71/7 = 10.1. The risk of dying from coronary thrombosis comparing smokers is 599/422 = 1.4. References: Friis and Sellers; p. 276 | Kleinbaum et al.; pp. 72-73 | Hebel and McCarter; pp. 29, 118 | Last et al.; p. 156

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Which measure of mortality would you calculate to determine the proportion of all deaths that is caused by heart disease? (A) Case fatality (B) Cause-specific mortality rate (C) Crude mortality rate (D) Proportionate mortality ratio (E) Potential years of life lost

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Which measure of mortality would you calculate to determine the proportion of all deaths that is caused by heart disease? (D) Proportionate mortality ratio PMR is calculated as the number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population. Reference: Friis, page 118

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The staff at the state health department Birth Defects Registry systematically visit the labor and delivery units of all hospitals in the state on an on-going basis and review their records to identify major congenital malformations. This is an example of: (A) Sentinel surveillance (B) Active surveillance (C) Passive surveillance (D) Syndromic surveillance (E) Reportable conditions

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The staff at the state health department Birth Defects Registry systematically visit the labor and delivery units of all hospitals in the state on an on-going basis and review their records to identify major congenital malformations. This is an example of: (B) Active surveillance Active surveillance refers to a system in which project staff make periodic visits to clinics and hospitals to identify new cases of disease that have occurred (case finding). Reference: Gordis, page 54

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Which of the following statements is true about surveillance data? (A) It cannot be used to detect geographical clusters (B) It includes information on health outcomes, but not exposures or risk factors (C) It provides early recognition of an infectious disease outbreak, but is much less useful for non-infectious disease events (D) It can be used to monitor temporal trends in disease (E) It only includes data pertaining to vaccine-related diseases

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Which of the following statements is true about surveillance data? (D) It can be used to monitor temporal trends in disease Monitoring temporal trends in disease is a primary function of surveillance systems. While surveillance historically, and perhaps more frequently, is conducted for infectious diseases, in recent years it has become increasingly important in monitoring changes in other types of conditions, such as cancer, congenital malformations, asthma, occupational exposures and diseases, and injuries and illness after natural disasters. Reference: Gordis page 54

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The following are characteristics of a cross-sectional study except: (A) Characteristics of "case" are clearly defined (B) The study is done on a defined population (C) All members of the population should be able to experience the outcome of interest (D) Patients are followed for a sufficient period of time for outcome events to occur (E) The study is done on a representative sample of the target population

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The following are characteristics of a cross-sectional study except: (D) Patients are followed for a sufficient period of time for outcome events to occur Patients are not followed in a cross-sectional study.

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All of the following statements are true about both prospective and retrospective cohort studies except: (A) They measure the incidence of disease (B) They allow assessment of possible associations between exposure and many outcomes (C) They require the manipulation of the exposure of interest by the investigator (D) They avoid bias that might occur if measurement of exposure is made after the outcome of interest is known

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All of the following statements are true about both prospective and retrospective cohort studies except: (C) They require the manipulation of the exposure of interest by the investigator There is no manipulation of the exposure in a cohort study.

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In a cross-sectional study of peptic ulcer among men and women aged 35 to 59, 70 per 100,000 men and 95 per 100,000 women met the criteria for symptomatic peptic ulcer disease. The inference that in this age group, women are at greater risk of developing peptic ulcer is: (A) Correct (B) Incorrect because of failure to distinguish between incidence and prevalence (C) Incorrect because rates were used to compare males and females (D) Incorrect because of failure to recognize a possible cohort effect (E) Incorrect because there is no comparison or control group

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In a cross-sectional study of peptic ulcer among men and women aged 35 to 59, 70 per 100,000 men and 95 per 100,000 women met the criteria for symptomatic peptic ulcer disease. The inference that in this age group, women are at greater risk of developing peptic ulcer is: (B) Incorrect because of failure to distinguish between incidence and prevalence Prevalence does not represent risk.

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A prevalence study of depression drew a sample of the residents of Houston by visiting all residence in randomly selected census tracts. A screening test with a sensitivity of 99% and a specificity of 50% was used to identify individuals as "likely depressed." The study reported a prevalence of 28%. This prevalence is: (A) A true representation of depression in this population (B) Higher than expected because of the specificity of the screening test (C) Lower than expected because of the specificity of the screening test (D) Higher than expected because of the sensitivity of the test (E) Lower than expected because of the sensitivity of the test

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A prevalence study of depression drew a sample of the residents of Houston by visiting all residence in randomly selected census tracts. A screening test with a sensitivity of 99% and a specificity of 50% was used to identify individuals as "likely depressed." The study reported a prevalence of 28%. This prevalence is: (B) Higher than expected because of the specificity of the screening test Higher than expected because the specificity is so low there will be many false positives.

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