All are example for randomised control trials except-: (A) Natural experiments, (B) Clinical trials, (C) Risk factor trials, (D) Preventive trials
Answer is A. .the major type of randomised controlled trials includes, 1.clinical trials 2.preventive trials. 3.risk factor trials 4.cessation experimnts 5.trial of aetiological agents. 6.evaluation of health services. ref:park&;s textbook,ed 22,pg no 82