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18 Cards in this Set
- Front
- Back
2 reasons case-conrtol trials are susceptible to bias
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1) Extra step to select controls. 2) Both E and D are known and can influence both selection of subjects information accuracy
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3 conditions necessary for valid case-control study
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1) Identification of the study base. 2) Controls are random sample of study base. 3) Accurate nondifferential info on exposure and confounders.
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Identification of the study base
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1) All cases. 2) Random sample of cases if large number
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6 steps in a case-control study
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1) Identify Study Base. 2)Identify cases. 3) Identify controls. 4) Exposure. 5) Confounders. 6)Analysis
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3 keys for Disease: Cases
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1)Aspire for high Sens and Spec. 2) Restrict to newly developed disease (or dealing with survival). 3)Try and get ALL CASES (avoids selection bias)
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Controls
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random samples from study base
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Exposure: issues for case-control
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subjects enter study after disease occurrence. Pre-disease data needed.
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Analysis
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OR and RR estimates
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Study Base
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Underlying cohort and time-period where all cases are identified and controls are randomly samples. AKA - source cohort, reference population
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What IS NOT they study base
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Cases + Controls
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2 types of study base
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1) Primary. 2) Secondary
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Primary Study Base
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Explicit cohort where all cases and controls can be identified. Only info needed for idenficiation is: person and dates
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Nested case-control designs
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Random sample of controls from a primary study base. Could have been a cohort study at greater cost.
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EG. of primary study base
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1) Study conducted within an existing cohort or rct population. 2) Study conducted with medical care DB where a retro-cohort could be done
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EG. of NOT primary study base
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1) Population where cases are ascertained is ambiguously defined. 2) Well dfined but rosters do not define study base
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Seconday Study base
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Study base identified conceptually but no definitive roster. Selcting controls approximate random sampling.
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Danger of using a secondary study base
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Sampling is not random and introduces bias
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5 reasons to use a case-control study
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1) When cohort study not feasible (expense, time). 2)Brief transient exposures. 3) Outbreaks. 4)Primary study base is present. 5) Seconday study base approximates random sampling.
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