Epidemiology 101
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Measure of association between frequency of exposure and frequency of outcome used in a case-control study (ad)/(bc)
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Odds Ratio
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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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Ecologic Studies
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a measure of risk differences -In a cohort study, it refers to the difference between the incidence rate of disease in the exposed group and the incidence rate in the non-exposed group
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Attributable Risk
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a study that compares individuals who have a disease with individuals who do not have the disease in order to examine differences in exposures or risk factors for the disease
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Case Control Study
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Ratio of the risk of the disease or death among the exposed to the risk among the non-exposed Formula: Incidence rate in the exposed / incidence rate in the non-exposed
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Relative Risk
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A type of relationship between two entities in which change in one entity does not correspond with constant change in the other entity.
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Non-Linear Association
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Observational & Intervention
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Describe the two major approaches used in analytic studies.
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Observational: Some ecologic studies, case-control, cohort Intervention: Clinical Trial, Community Intervention
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What circumstances would merit the use of either observational and intervention in analytic studies?
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1. who manipulates the exposure factors? 2. How many observations are made? 3. what is the directionality of exposure? 4. What are the methods of data collections? 5. What is the timing of data collections? 6. What is the unit of observation? 7. How available are the study subjects?
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Seven factors that characterize study designs
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a small, relatively permanent statistical subdivision of a county or statistically equivalent entity -generally contains between 1,000 to 8,000 people -boundaries are delineated with the intention of being stable over many decades, so they generally follow relatively permanent visible features.
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Census Tract used by the U.S. Census Bureau
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an area bounded on all sides by visible and/or non-visivle features shown on a map prepared by the Census Bureau -a block is the smallest geographic entity for which the Census Bureau tabulates decennial Census data
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Census Block as used by the U.S. Census Bureau
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A large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus
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Metropolitan area as used by the U.S. Census Bureau
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In an ecologic study, the units of analysis are populations or groups of people rather than in a observational study where they are individuals.
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State one of the most important ways in which ecologic studies differ from other observational study designs used in epidemiology.
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A misleading conclusion about the relationship between a factor and an outcome that occurs when the observed association obtained between study variables at the group level does not necessarily hold true at the individual level.
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Ecologic Fallacy
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A study that compares individuals who have a disease with individuals who do not have the disease in order to examine differences in exposures or risk factors for the disease
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Case-Control Study
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an epidemiological experiment in which subjects in a population are randomly allocated into groups to receive or not receive an experimental preventative or therapeutic procedure, maneuver, or intervention. The results are assessed by rigorous comparison of rates of disease, death, recovery, or other appropriate outcomes in the study and control groups
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Randomized Control Trials
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Research in which the investigator manipulates the study factor but does not assign individual subjects randomly to the exposed & non-exposed groups
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Quasi-Experimential Designs
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a type of study that collects data and follows a group of subjects who have received a specific exposure. The incidence of a specific disease or other outcome of interest is tracked overtime. The incidence in the exposed group is compared with the incidence in groups that are not exposed, that have different levels of exposure, or that have different types of exposures.
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Cohort Studies
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-exposure factor -observations made -methods for collecting data -timing of data collection -units observed -availability of study subjects
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State three ways in which study designs differ from one another.
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one that has several peaks in the frequency of a condition
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Multimodal Curve
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indicates the difference between two hypotheses are significantly difference with certain probability
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Statistical Significance
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no probability is involved. The outcome of an experiment is observed as is
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Practical/Clinical Significance
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Power is "the ability of a study to demonstrate an association if one exists". Among the factors related to power are sample size and how large an effect is observed.
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How does power apply to statistical testing?
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-A parameter is a number obtained by calculations from a population -A statistic is a number calculated from a sample. A statistic is usually used to estimate a parameter
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What is the difference between a parameter and a statistic?
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Strength Consistency Specificity Temporality Biological Gradient Plausibility Coherence Experiment Analogy
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Criteria of Causality
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refers to a linkage between or among variables; variables that are associated with one another can be positively or negatively related
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Association
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as the value of one variable increases so does the value of the other variable
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Positive Association
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When the value of one variable increases, the value of the other variable decreases
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Negative Association
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Scatter Plots & Contingency Tables
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Two methods for displaying data graphically
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Non-Causal: (X does not cause Y) Causal: (X causes Y)
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Distinguish between Non-causal and causal association.
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a point is a specific number while an interval is a range. -The point estimate is an actual value. -The confidence interval estimate is an acceptable range of values
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Distinguish between a point estimate and a confidence interval estimate.
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is a type of correlative association between an exposure (dose of toxic chemical) and effect (biological outcome).
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Dose-Response Relationship
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P < .05 (can not be .051) (If we do a study over and over again, our chance of getting the results we want is 95% (5x out of 100). -Interval can not contain 1
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Example of how Chance affects epidemiological associations
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Classifies the occurrence of disease according to person, place, time variables ** "concerned with characterizing the amount and distribution of health and disease within a population."
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Descriptive Epidemiology
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Case reports, Case Series, Cross-Sectional Studies
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Types of Descriptive Epidemiological Studies
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*Case reports: adverse reactions due to cosmetic surgery in the US *Case Series: reported cases of primary meningoencephatlits (121 cases reported between 1937 and 2007) *Cross-Sectional Studies: A type of prevalence study. The Behavioral Risk Factor Surveillance System (BRFSS)
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What are the uses of the types of descriptive epidemiological studies
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-provides a basis for generating hypotheses -connect intimately with the process of epidemiological inference -initiated with descriptive observations
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Describe the process of epidemiologic inference in the context of descriptive epidemiology.
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Person: Age & Sex Place: International (WHO) & National (within country) Time: Secular trends & Cyclic (seasonal) trends
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Two examples of person, place, and time variables.
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accounts of a single occurrence of a noteworthy health-related incident or of a small collection of such events
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Case Reports
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a larger collection of cases of diseases, often grouped consecutively and listing common features: e.g. characteristics of affected patients
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Case Series
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white, black or african american, american indian & Alaska native, asian, native hawaiian and other pacific islanders
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what are the racial/ethnic classifications used to describe health characteristics?
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1. lower frequency of asthma reported among hispanics 2. incidence of gonorrhea is higher among non-hispanic blacks than other groups
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Name two conditions that vary according to race/ethnicity.
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differences in the occurrence of diseases and adverse health conditions in the population
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Health Disparities
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Using the person, place, and time variables helps to determine who or what, when, and where to determine the overall problem and where is might have began and where it could stop.
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How could using descriptive epidemiological studies examine the obesity epidemic in the United States?
