All are example for randomised control trials except-
Natural experiments
Clinical trials
Risk factor trials
Preventive trials
.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
Epidemiology