Epidemiology Ch. 7 Cohort Studies – Flashcards
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Cohort
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A group of individuals who share an exposure in common and who are followed over time
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Temporality
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Timing of information about cause and effect; whether the information about cause and effect was assembled at the same time point or whether information about the cause was garnered before or after the information about the effect
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What do observational studies have a difficult time demonstrating?
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Difficult time demonstrating temporality
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YPLL
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A type of statistical measure that takes into account the effect of premature death caused by diseases
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Relative Risk
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Ratio of the risk of disease or death among the exposed to the risk among unexposed
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Formula: Relative Risk
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Incidence rate in the exposed / Incidence rate in the nonexposed
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Cohort Life Table
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A table that presents mortality statistics of all persons born during a particular year
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Cohort Analysis
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Tabulation and analysis of morbidity or mortality rates
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Cohort Effect
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Consequence of long-term secular trends in exposure within a specific cohort
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DALYs
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A measure that adds the time a person has a disability to the time lost to early death (ex: military)
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Info. required for survival curve
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Time of entry into study Time of death or other outcome Status of patient at time of outcome
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Survival Curves
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A method of portraying survival times. Useful in infectious diseases, clinical trials, and psychiatric disorders.
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Lethality Curves
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Inverse nature of a survival curve
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3 variations in Cohort Designs that depend on timing
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Prospective Retrospective Historical Prospective aka ambispective
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Timing of data collection for 3 variations of Cohort designs
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Prospective exposure present disease future Retrospective exposure past disease present Historical Prospective exposure past and/or present disease future
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Historical Prospective Cohort Study
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A design that makes use of both retrospective features and prospective features. AKA ambispective cohort study
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Nested case-control study
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A type of research design wherein both cases and controls come from the population of a cohort study
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Cohort Study
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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 over time. The incidence in the exposed group is compared with the incidence in the groups that are not exposed, have different levels of exposure, or have different types of exposures.
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Cohort Studies
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Permit calculation of incidence rates (risk of development of disease due to exposure). Can be thought of as going from cause to effect. Involve collection of primary data (exposure data).
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2 Strategies of Cohort Studies
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Population-based and exposure-based
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Population-Based Cohort Studies
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Cohort includes entire population or a representative sample of the population. Example: Framingham Coronary heart disease study
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Exposure-Based Cohort Studies
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Cohort made of subjects with a common exposure. Example: Workers exposed to lead during battery production. Useful for rare exposures.
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Practical consideration regarding cohort studies
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Availability of exposure data Size and cost of the cohort used Data collection and data management Follow-up issues Sufficiency of scientific justification
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Types of follow-up and defintions
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Active follow-up: Investigator through direct contact with the cohort, must obtain data on subsequent incidence of the outcome. Through mailings, phone calls, written invitations. Passive follow-up: Doesn't require direct contact with cohort members. Outcomes collected by organizations outside the investigative team.
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Only observational study that permit examination of multiple outcomes
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Cohort Studies
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Advantages of Cohort Studies
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Permit direct determination of risk. Time sequencing of exposure and outcome. Can study multiple outcomes. Can study rare exposures.
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Limitations of Cohort Studies
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Take a long time. Costly. Subjects lost to follow-up
