Case-control studies are observational and travel the reverse path of the cohort: they start from the outcome and look backwards for the exposure. They are the studies of odds measures.
The case-control study looks backwards: from today’s outcome to yesterday’s exposure.
From the same source population as the cases, with the same chance of exposure — poor control selection is the biggest source of bias.
Up to about 4 controls per case increase statistical power; beyond that the gain is minimal.
It is the ideal design: it gathers existing cases without waiting years of follow-up.
Written by Francisco Tustumi, digestive system surgeon (FMUSP), associate editor of ABCD.
Developed by Surya MKT