The randomized controlled trial is one of the simplest but most powerful tools of research. In essence, the randomized controlled trial is a study in which people are allocated at random to receive one of several clinical interventions On most occasions, the term “intervention” refers to treatment, but it should be used in a much wider sense to include any clinical maneuver offered to study participants that may have an effect on their health status. Such clinical maneuvers include prevention strategies, screening programs, diagnostic tests, interventional procedures, the setting in which health care is provided, and educational models. Randomized controlled trials in radiology can play a major role in the assessment of screening programs, diagnostic tests, and procedures in interventional radiology. Randomized controlled trials are used to examine the effect of interventions on particular outcomes such as death or the recurrence of disease. Some consider randomized controlled trials to be the best of all research designs, or “the most powerful tool in modern clinical research”, mainly because the act of randomizing patients to receive or not receive the intervention ensures that, on average, all other possible causes are equal between the two groups. Thus, any significant differences between groups in the outcome event can be attributed to the intervention and not to some other unidentified factor. However, randomized controlled trials are not a panacea to answer all clinical questions; for example, the effect of a risk factor such as smoking cannot ethically be addressed with randomized controlled trials. Furthermore, in many situations randomized controlled trials are not feasible, necessary, appropriate, or even sufficient to help solve important problems. Randomized controlled trials are not appropriate for cancer screening, a situation in which the outcome is rare and frequently occurs only after a long delay. Thus, although the test for appraising the ultimate value of a diagnostic test may be a large well-designed randomized controlled trial that has patient outcomes as the end point, the trial should presumably be performed after other smaller studies have examined the predictive value of the test against some accepted standard.
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