This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
True of case control studies 
Select and explain. 
A. It proceeds from cause to effect, B. Odds ratio can be calculated, C. Incidence can be calculated, D. Needs many patients
B: Odds ratio can be calculated
Answer: B: Odds ratio can be calculated 
Explanation: <p>case control studies usually known as retrospective studies.are those which proceeds from efect to cause .it mainly involves two study populations cases and controls.they are basically comparison studies from which the"odds ratio" can be calculated.focus is on a health problem that has already occurred.not much patients are required for the study.ODDS RATIO is a measure of the strength of association between risk factor and outcome.it is closely related to relative risk.</p><p>ref:park&;s textbook of preventive and social medicine,22 nd edition ,pg no 68</p>