1. The following statement is wrong regarding case control study
A it is useful for rare disease
B Early to do the study
C Incidence can be calculated
D It is a retrospective study 

Ans. C Incidence can be ...
> We cannot measure incidence, and can only estimate the relative risk.
Case control studies, often called ‘retrospective studies’ are a common first approach to test casual hypothesis.
 Case - control study or retrospective study has 3 features:
>Both exposure and out come have occurred before the start of study.
>The study proceeds backwards from effect to cause, (so called retrospective study)
> It uses a control group to come to inference.
> Matching of cases and controls to eliminate confounding factors is done in this study.
>Relative risk & odds ratio can be calculated but not incidence.