In a case control study, the most characteristic feature is -

Ans. is 'a' i.e., Odds ratio estimation o Final step in case control study is analysis to find out ? i) Exposure rates among cases and controls to suspected factor. ii) Estimation of disease risk associated with exposure (odds ratio). i) Exposure rates o A case control study provides a direct estimation of the exposure rates (frequency of exposure) to a suspected factor. ii) Odds - ratio (cross product ratio) o From a case control study odds ratio can be derived which a measure of the strength of association between risk factor and outcome. o Odds ratio is closely related to relative risk (which is analysed in coho study) --> odds ratio represents only an estimate of relative risk. o The odds ratio is cross product of entries in above table o Odds ratio is a key parameter in analysis of case control studies. Why is it not possible to estimate relative risk in case-control study ? o Relative risk is the ratio between the incidence of disease among exposed and incidence among non-exposed. o So, for relative risk estimation, incidence rate is required. o But incidence rate can not be calculated by case control study as there is no denominator (poulation at risk). o Because both disease and exposure have already occured, there is no risk for the subjects in the study --> There is no population at risk.