Cohort studies may by fixed or dynamic, the first beginning at one point in time of recruitment, the latter having recruitment over a period of time, with implications for the complexity of analysis and interpretation of results.
Outcome
positive (cases) | negative (controls) | |
exposure | a | b |
non-exposure | c | d |
The direction of enquiry may thus be drawn: Cause ---------------------------> Effect
A study may be prospective, where the investigators have to wait for the result, or retrospective, where there is certainly less wait, but there are problems with mortality and bias.
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