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6 Cards in this Set
- Front
- Back
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5 common sources of bias in a case-control study
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1) Failure to randomly sample from the study base (Selection bias). 2) Incomplete disease ascertainment (selection bias). 3) Exposure misclass (differential information bias) 4) Confounder misclass (differential information bias) 5)Chance (inadequate power)
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Failure to randomly sample study base
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control group has artificially higher or lower prevalence of exposure. Eg. Estrogens and MI: if use trauma controls it will include women with osteoporotic fractures (Estrogens could be low).
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Disease ascertainment
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Cases and controls recruited separately - selection related to the exposure. To overcome identify all cases within a catchment
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Exposure
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Exposure is measured after disease. Source of information bias for cases
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Confounding
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measured after disease
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Chance
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need massive numbers for good power but usually not a major problem
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