Principles of Epidemiology Exam 1 – Flashcards
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Epidemiology
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Study of distribution and determinants of disease in population
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Open population
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population membership may change over period of interest, members can be lost or added use incidence rate or incidence density
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Closed population
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population membership remains stable over period of interest, no members added or lost use cumulative incidence
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Primary prevention
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action taken to prevent the development of a disease in a not-yet-diseased person
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Secondary prevention
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early detection of existing disease to reduce severity and complications
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Tertiary prevention
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reducing the impact of the disease
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Prevalence
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how common is a given disease as of a certain time
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Prevalence proprtion
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number of prevalent cases/size of population at that time
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Incidence
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how often does disease occur over a period of time
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Incidence ratio
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number of cases/population at risk
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Cumulative incidence
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proportion of initially susceptible in a closed population who became incident cases during time period
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Incidence proportion Attack rate
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number of incident (new) cases/ number of persons initially at risk
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Incidence rate
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the count of incident cases divided by the aggregate amount of at risk experience from which they arose
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Incidence density
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number of incident cases / amount of at risk experience (units are person-time)
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Mortality
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incidence of fatal cases of disease in population at risk for dying
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Mortality ratio
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number of deaths / anyone at risk for death
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Case fatality
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incidence of death from a disease among persons who develop the disease
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Case fatality rate
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number of fatal cases / total number of cases
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Descriptive studies
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case reports and case series undertake without a specific hypothesis in mind
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Analytic studies
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observational or experimental employed to test a hypothesis
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Case reports
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detailed presentation of a single case important for documenting new diseases (can lead to hypothesis generation)
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Case series
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study of a larger group with a particular disease way of deliniating the clinical picture of a disease
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Ecological studies
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use data from entire population to compare disease frequencies among groups unit of analysis is the aggregate
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Ecological fallacy
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thinking that relationships observed for groups hold for individuals
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Ecological studies
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Limitations: usually no control for confounding no information on individuals use an average measure of exposure Strengths: in a large population you have a wider range of exposure
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Cross-sectional studies
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Exposure an disease status of individual measured at one point in time "prevalence studies"
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Cross-sectional studies
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Limitations: temporality - can't determine timeline of exposure to disease associations don't represent incidence of disease - just chronicity potential for missclassification of disease because of remissions/exacerbations Strengths: reasonably good generalizability data on individuals, not groups cost and time efficient
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Cohort studies
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compares the incidence of disease over time among groups that differ in exposure enrollment in study is based on exposure of interest
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Prospective cohort study
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cohort study where outcome has yet to occur and you follow over time
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Retrospective cohort study
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cohort study where outcome has already occurred like a reconstruction of a cohort study that has already happened
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Cohort studies
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Limitations: not good for rare disease not good for studying multiple exposures Strengths: can estimate actual incidence (because follows over time) possible to study multiple outcomes good for studying rare exposures
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Case-control studies
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compares the frequency of past exposure between cases who develop the disease and controls who don't enrollment in study is based on outcome
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Case-control studies
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Limitations: bad for rare exposures can't study multiple outcomes can't estimate actual incidence (retrospective memories of event) Strengths: good for studying rare diseases good for studying multiple exposures quick answers because both outcome and exposure have already occurred
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Randomized control trials
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researcher assigns exposure (randomized to control for confounding) 2 arms - treatment and control
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Counterfactual
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the scenario that doesn't actually occur (e.g. not smoking for 20 years if a smoker for 20 years)
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Relative risk
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measure of disease association in cohort studies
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Relative risk
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incidence in exposed / incidence in unexposed (a/(a+b))/(c/(c+d))
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Relative risk interpretation
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=1 -> risk is equal in both exposure groups >1 -> risk is greater in exposed than unexposed risk is greater in unexposed than exposed
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Odds ratio
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measure of disease association in case-control (mainly) and cohort studies
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Odds ratio
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odds that an exposed person becomes a case / odds that an unexposed person becomes a case (a x d)/(b x c)
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Attributable risk
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difference in rate of disease between the exposed and unexposed populations
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Attributable risk
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Incidence in exposed - incidence in unexposed (can be expressed as a percentage of incidence in exposed)
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Population attributable risk
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proportion of the incidence of disease in population due to exposure
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Population attributable risk
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Incidence in total population - incidence unexposed (can be expressed as a percentage of incidence in total population)
