<prompt> Which of the following statement is true -Case control study is not suitable for rare diseasesCohort study involves large number of subjectsCase-control study is relatively expensiveCohort study yields relatively quick results  <response>: Ans. is b i.e., Cohort study involves large number of subjects Prevalence of blindness in India: 700 per 1 lakh population 0.7 if cut of criteria is 360 WHO criteria; or 1100 per lakh population 1.1 if cut of criteria is 660 NPCB criteria. 