Case Control Studies

Case control studies Both exposure and outcome occurred The study proceeds backwards Uses control or comparison group to support or refute inference.

Basic design Risk factor

cases

Controls

present

a

b

absent

c

d

Basic steps • • • • •

Selection of cases and controls Matching Measurement of exposure Analysis interpretation

Bias in case control studies • • • • •

Bias due to confounding Recall bias Selection bias Berksonian bias Interviewers bias

advantages • • • • • • • •

Relatively easy Rapid and inexpensive Require a few subjects Suitable for rare disease No risk to subjects Multiple risk factors studied Prevention & control established No attrition, ethical problem minimal

disadvantages • • • • • •

Problem of bias Accuracy is uncertain Appropriate control selection difficult Incidence cant be measured Do not distinguish between cause & risk Not suited to evaluate therapy.