True regarding case control study are all of the following except: March 2010

Ans. D: Attributable risk can be Case-control is a type of epidemiological study design in which individuals with a defined characteristic (often, a specific diagnosis, perhaps lung cancer) are matched with people who do not have the condition but are otherwise similar (the 'controls'). Fuher data is then collected on those individuals and the groups are compared to find out if other characteristics (perhaps a history of smoking) are also different between the two groups. They have pointed the way to a number of impoant discoveries and advances, but their retrospective, non-randomized nature limits the strength of their conclusions. However, coho studies and randomized controlled trials, which provide stronger evidence, usually take much more time and money. Case-control studies are a relatively inexpensive and frequently-used type of epidemiological study that can be carried out by small teams or individual researchers in single facilities over a relatively sho period of time. Ethical approval is more easily obtained for an observational rather than an experimental study. One of the most significant triumphs of the case-control study was the demonstration of the link between tobacco smoking and lung cancer. Case control generally yields only estimate of odd's ratio, whereas coho's study yields incidence rates, relative risk as well as attributable risk.