True regarding coho's study are all of the following except: September 2007

Ans. C: Odd's ratio can be calculated Coho study is often undeaken to obtain evidence to try to refute the existence of a suspected association between cause and effect. Crucially, the coho is identified before the appearance of the disease under investigation. The study groups, so defined, are observed over a period of time to determine the frequency of new incidence of the studied disease among them. The coho cannot therefore be defined as a group of people who already have the disease. Coho studies can either be performed prospectively or retrospectively from historical records. Prospective (longitudinal) coho studies between exposure and disease strongly aid in studying causal associations. The advantage of prospective coho study data is the longitudinal observation of the individual through time, and the collection of data at regular intervals, so recall error is reduced. However, coho studies are expensive to conduct, are sensitive to attrition and take a long follow-up time to generate useful data. Neveheless, the results that are obtained from long-term coho studies are of substantially superior quality to retrospective/cross-sectional studies, and coho studies are considered the gold standard in observational epidemiology. Moreover, coho studies are informative for efficiently studying a wide-range of exposure-disease associations. It is the most reliable mean of showing an association between a suspected risk factor and subsequent disease because it eliminates many of the problems of the case control study. Odd's ratio can be derived from a case control study, which is a measure of the strength of the association between risk factor and outcome.