Comparison of an outcome (e.g. morbidity or mortality) between two groups of people deliberately subjected to different dietary or drug regimes.
A comparison of the outcome between two or more groups of patients that are deliberately subjected to different regimes (usually of treatment but sometimes of a preventive measure, such as vaccination). Wherever possible those entering the trial should be allocated to their respective groups by means of random numbers, and one such group (controls) should have no active treatment (randomized controlled trial). Ideally neither the patient nor the person assessing the outcome should be aware of which therapy is allocated to which patient {blind trial), nor should the doctor responsible for treatment {double-blind trial), and groups should exchange treatment after a prearranged period (cross-over trial).
Comparison of outcomes between two or more groups of patients who have been intentionally given different treatments or preventative measures for example, diets. The subjects in the trial should be randomly allocated to the groups, with patients in one group called controls receiving no active treatment. If possible, neither patients nor doctors participating in a study should know which patients are receiving what treatment (double bling study/trial). Furthermore, groups should exchange treatments after a prearranged time.