All of the following are true about case control study, EXCEPT:

Ans. is 'b' Relative risk can be calculated Relative Risk = (Incidence among exposed / Incidence among non-exposed ) x 100A typical case control study does not provide incidence rates from which Relative Risk can be calculated directly because there is no appropriate denominator or population at risk to calculate these rates.In General, the Relative Risk can be exactly determined only from a cohort study.From case control we can derive what is known as odd's ratio which is a measure of strength of association between Risk factor and outcome.Advantages and disadvantages of case control studiesAdvantagesRelatively easy to carry outRapid and inexpensiveRequire comparatively few subjectsParticularly suitable to investigate rare diseaseNo Risk to subjectsAllow study of several aetiological factorsRisk factors can be identifiedDoes not require follow upEthical problems minimalDisadvantagesProblem of bias relies on memory or past recordsSelection of control difficultWe cannot measure incidence, only estimate Relative RiskDo not distinguish between cause and associated factorsNot suited to the evaluation of therapy or prophylaxis of disease.