All of the following are characteristics of case control study except -

Ans. is 'b' i.e., Measures incidence rate o Incidence rate can not be measured by case-control study as denominator (population at risk is not available).ADVANTAGES1. Relatively easy to carry out.2. Rapid and inexpensive (compared with cohort studies).3. Require comparatively few subj ects.4. Particularly suitable to investigate rare diseases or diseases about which little is known.5. No risk to subjects6. Allows the study of several different aetiological factors (e.g., smoking, physical activity and personality characteristic in myocardial infarction).7. Risk factors can be identified. Rational prevention and control programmes can be established.8. No attrition problems, because case control studies do not require follow'-up of individuals into the future.9. Ethical problems minimal.DISADVANTAGES1. Problems of bias relies on memory or past records, the accuracy of which may be uncertain; validation of information obtained is difficult or sometimes impossible.2 Selection of an appropriate control group may be difficult.We cannot measure incidence, and can only estimate the relative risk (odds ratio).Do not distinguish between causes and associated factors.Not suited to the evaluation of therapy or prophylaxis of disease.Another major concern is the representativeness of cases and controls.