Case-control studies: starting from the outcome

A case-control study starts from the outcome. Find people with the disease, find comparable people without it, and compare their past exposures. In conflict-torn Yemen, a matched case-control study linked cholera to unwashed khat and common-source water within weeks. The design suits rare outcomes and outbreaks, and choosing controls is where it goes wrong: a control should be someone who would have been counted as a case had they fallen ill. Matching controls confounding but can't be ignored in the analysis, and people who are sick tend to remember their exposures differently.

Also covered: control selection · matching and over-matching · recall bias · nested case-control studies

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Lesson 3 · 6 steps

1What descriptive designs can and cannot tell us7:16 2Cross-sectional studies and the problem of timing4:51 3Case-control studies: starting from the outcome6:21 4Cohort studies: following people forward in time6:39 5Controlling confounding in observational data7:49 6Choosing and reading an observational design6:45

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