[The Comprehensive Cohort Design as alternative to the randomized controlled trial in rehabilitation research:...

In rehabilitation research new therapies have to be evaluated within randomized trials as the best choice for proving the efficacy. Randomized controlled trials are widely accepted as the definitive method for evaluating the efficacy of new therapies. The random assignment of patients to their treatment ensures the internal validity of the comparison of new treatments with controls. Often patients in a randomized trial only represent a small proportion of the patients who satisfy the inclusion criteria of the trial. This will especially be true in rehabilitation medicine because of strong preferences of the patients for one or the other therapy. An assessment of the external validity of trial results can best be achieved by comparing the study population to the population of patients who met the eligibility criteria but did not consent to randomization. The Comprehensive Cohort Design (CCD) is designed to have the opportunity of recruiting all patients fulfilling these eligibility criteria regardless of their consent to randomisation. Advantages and disadvantages of this study design will be discussed in detail and on the example of the SARAH-study.