feb_26_16 - POPM 3240*01 Cross-sectional studies Temporal...

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POPM 3240*01 February 26, 2016 Cross-sectional studies Temporal problems --> cannot tell whether exposure or outcome occurs first May not be able to infer causality, esp. with non-permanent characteristics Definitely shows a statistically significant association, if one exists, but does not determine causality Bias Confounders particularly important Cohort studies Cohort --> group with defined characteristics in common Typically in epidemiological studies, cohort is based on exposure status Select subjects based on exposure status Define groups based on E+ and E- groups All subjects must be O- at the start of the study Follow groups over a predetermined period of time to estimate incidence of disease (new cases) Compare development of disease in E+ and E- groups Observational --> investigator does not determine or allocate exposure status Selecting study population Select subjects based on exposure status Or, select a study population and classify based on exposure status Still a cohort study because all of our subjects are D- at start, and followed over time Time Sequence Prospective --> follow groups forward in time from the present to a predetermined end point Retrospective --> follow groups from a time in the past, either to present day, or more recent records Create historical cohorts from records, typically quicker and cheaper, but less complete than
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