Case control study used to measure:

Ref: Park 'Textbook of Preventive and Social Medicine', 22nd edition, Pg: 75Explanation:List of FormulaIncidence rate=Number of new cases of specific disease during a given time periodPopulation at risk during that periodx 1000Relative risk=Incidence among exposed Incidence among unexposedAttributable risk=incidence among exposed - incidence among unexpectedIncidence among: exposedx 100=adbcOdds ratioIncidence rate can be calculated only it1. A study starts with a disease free population2. The study follows this disease free populationBoth these conditions are not satisfied in a case control study - where you start with group of people with disease (case) and without disease (control).There is no component of follow' up. So you cannot find out incidence.From the above formula it is obvious that you need incidence rate to calculate relative risk and attributable risk.Hence is case control study you can calculate only odds ratio