Chapter 7- Analytic Epidemiology – Flashcards
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Why is analytic epidemiology important to society?
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analytic studies lead to the prevention of disease
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Framingham Study
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contributed to our understanding of risk factors associated with coronary heart disease, which has lead to a reduction in morbidity and mortality from CHD
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What is the difference between analytic and descriptive epidemiology?
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analytic is concerned with the etiology of diseases and other health outcomes, while descriptive classifies a diseases or other health outcome according to the categories of person, place, and time
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what are the two sub categories to analytic epidemiology
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observational and experimental studies
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what kind of studies are included in observational studies?
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-ecological -case control -cohort
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What are the three types of cohort studies
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prospective, retrospective and historical prospective
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what are the two types of experimental studies
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clinical trials and community interventions
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quasi-experimental study
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one in which the investigator is able to control the exposure of individuals or units to the factor but is unable to assign participants randomly to the conditions of the study
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list the factors that characterize design studies
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- who manipulates the exposure factor -the number of observations made -directionality of exposure - data collection methods -timing of data collection -unit of observation -availability of subjects
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directionality of exposure
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measurement relative to disease varies according to the type of study design used
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retrospective
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obtaining information about exposures that occurred in the past; often used in case controlled studies
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single point in time
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the study is referenced about a single point in time, as in a survey or taking a snapshot of the population; often used in cross sectional studies
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prospective approach
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information about the study outcome is collected in the future after the exposure has occurred -used by experimental and cohort studies
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data collection methods
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some methods require almost exclusive use of existing, previously collected data, whereas others require collection of new data
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what type of data is often used by ecological studies?
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existing data
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timing of data collection
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information is obtained about exposures that occurred in the past.
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unit of observation
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can be the individual or an entire group
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availability of subjects
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certain classes of subjects may not be available for research due to several reasons such as ethical issues
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ecological study
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a study in which the units of analysis are populations or groups of people rather than individuals
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what types of groups might be selected for an ecological study
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nations, states, census tracts, or counties
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ecologic comparison study
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involves an assessment of the association between exposure rates and disease rates during the same time period
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ecologic correlation
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association between two variables measured at the group level
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what is a deficiency of the ecologic technique
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uncontrolled factors
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ecologic fallacy
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erroneous inference that may occur because an association observed between variables on an aggregate level does not necessarily represent or reflect the association that exists at an individual level
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what is the advantage of ecologic studies
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-may provide information about the context of health -can be performed when individual level measurements are not available -can be conducted rapidly and with minimal resources
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what are the disadvantages of ecologic studies
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-ecologic fallacy -imprecise measurement of exposure
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case-control study
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one in which the subjects are defined on the basis of the presence or absence of an outcome of interest - the cases are those individuals who have the outcome or disease of interest, where as the controls do not - can only examine a single outcome or a limited set of outcomes
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matched case-control study
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one in which the cases and controls have been matched according to one or more criteria such as sex, age, race, or other variables
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what is an advantage of case control studies
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they can examine many potential exposures, such as exposure to toxic chemicals, use of medications, or adverse lifestyle characteristics
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odds ratio
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measure of the association between frequency of exposure and frequency of outcome used in case-control studies
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why is the odds ratio called an indirect measure of risk
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because incidence rates have not been used; instead the risk of an outcome associated with an exposure is estimated by calculating the odds of exposure among the cases and controls
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what does an odds ratio of more than 1.0 suggest?
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a positive association between the exposure and disease or other outcome
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what does an odds ratio of less than 1.0 suggest?
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indicates that the exposure might be a protective factor
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protective factor
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is a circumstance or substance that provides a beneficial environment and makes a positive contribution to health
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what is suggested when the odds ratio is equal to 1.0
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there is no association between exposure and outcome
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what are the advantages of a case-controls study
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-can be used to study low prevalence conditions -relatively quick and easy to complete -usually inexpensive -involve smaller numbers of subjects
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what are the disadvantages of case-control studies?
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-measurement of exposure may be inaccurate -representativeness of cases and controls may be unknown -provide indirect estimates of risk -the temporal relationship between exposure factor and outcome cannot always be ascertained
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cohort studies
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tracks the incidence of a specific disease or other outcomes over time
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what are some variations of cohort studies
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prospective (longitudinal), retrospective, population based, exposure based
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cohort
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population group, or subset thereof that is followed over a period of time
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what is an example of a cohort
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-birth or age cohort -work cohort: people in a particular type of employment -school/educational cohort: people who graduated during a particular year
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what are the two major categories of cohort studies
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population based and exposure based
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population based cohort study
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leverages information from a total population or a representative sample of a population
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exposure based cohort study
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compares cohorts with or without different exposures -ex: two exposure groups (one is exposed and the other is not)
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prospective cohort study
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subjects are classified according to their exposure to a factor of interest and then observed over time to document the occurrence of new cases of disease or other health events
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longitudinal design
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subjects are followed over an extended period of time
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retrospective cohort study
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one that makes use of historical data to determine exposure level at some baseline in the past; follow-up for subsequent occurrences of disease between baseline and the present is performed
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what is the difference between a retrospective cohort and a case-control study
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entire cohort of exposed individuals is examined, in contrast a case control makes use of a limited number of cases and controls who usually do not represent an entire cohort of individuals
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relative risk
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the ratio of the incidence rate of a disease or health outcome in an exposed group to the incidence rate of the disease or condition in a non-exposed group
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incidence rate
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risk of occurrence of an outcome that is associated with a particular exposure
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what are the two measures of risk difference?
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attributable risk and population risk difference
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attributable risk
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refers to the difference between the incidence rate of a disease in the exposed group and the incidence rate in the non-exposed group
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population risk difference
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the difference between the rate of disease in the non-exposed segment of the population and the overall rate in the population
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what are the advantages of a cohort study
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-permit direct observation of risk -exposure factor is well defined -can study exposures that are uncommon in the population -the temporal relationship between factor and outcome is known
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what are the disadvantages of cohort studies
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-expensive and time consuming - complicated and difficult to carry out -subjects may be lost to follow up during the course of the study -exposure can be misclassified
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intervention study
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investigation involving intentional change in some aspect of the status of the subjects -e.g introduction of a preventive or therapeutic regimen or an intervention designed to test a hypothesized relationship
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clinical trial
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research activity that involves the administration of a test regiment to humans to evaluate its efficacy or its effectiveness and safety
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prophylactic trial
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designed to test preventative measures
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therapeutic trials
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evaluate new treatment methods
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what is the first phase of clinical trial
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initial human testing for safety
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what is the second phase of a clinical trial
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evaluate the immune responses of a limited group of vaccine recipients
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what is the third phase of a clinical trial
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large scale study involving randomization of participants to test and control conditions
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randomization
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process whereby chance determines the subject's' likelihood of assignments to either an intervention group of a control group
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randomized control trial
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clinical epidemiological experiment in which subjects are randomly allocated into groups usually called test and control groups, to receive or not to receive a preventive or a therapeutic procedure or intervention
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crossover design
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participants may be switched between or among treatment groups
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single blind study
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the subjects are unaware of whether they are participating in the treatment or control conditions
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double blind study
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neither the participants nor the investigators are aware of who has been assigned to the treatment or control conditions
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program evaluation
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the determination of whether the program meets stated goals and is justified economically
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Stanford Five City Project
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sought to reduce the risk of cardiovascular diseases, the trial was a media based campaign directed at Monterey and Salinas, California.
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external validity
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refers to one's ability to generalize from the results of the study to an external population
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internal validity
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refers to the degree to which the study has used methodologically sound procedures
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bias
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systematic deviation of results or inferences from the truth
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Hawthorne effect
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participants behavioral changes as a result of their knowledge of being in a study
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recall bias
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the fact that cases may remember an exposure more clearly than controls
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family recall bias
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occurs when cases are more likely to remember the details of their family history than are controls
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selection bias
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bias in the estimated association or effect of an exposure on an outcome that arises the from procedures used to select individuals into the study
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healthy worker effect
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observation that employed populations tend to have a lower mortality experience than the general population
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confounding
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the distortion of a measure of the effect of an exposure on an outcome due to the association of the exposure with other factors that influence the occurrence of the outcome
