Randomized controlled trials, however, are generally undertaken by experts in a particular disease area, in highly selected populations of participants, and involve a limited number of participants for a nite (o en relatively brief) period of time. In clinical practice the intervention will, almost inevitably, be used in a more heterogeneous population of patients, by less expert practitioners, and o en for much longer periods of time. e extent to which the ndings from randomized controlled trials can be generalized to disparate patient populations – o en referred to as external validity – has become of increasing concern.2-4
ree broad inuences may limit the generalizability of a randomized controlled trial:
■ the setting in which the trial has been carried out; ■ the patient population enrolled into the study; ■ the special characteristics of the intervention.