THE IMPACT OF PATIENT PREFERENCE ON THE DESIGN AND INTERPRETATION OF CLINICAL-TRIALS

Research on several health problems shows that patients and health car e providers do not use the same criteria to evaluate the effectiveness of treatment and often disagree on the severity of symptoms. When the disease is chronic and the main aim of treatment is to improve qualit y of life, we argue that variables rated as important by patients shou ld be used as outcomes in clinical trials, and that in most cases thes e need to be measured from subjects' self-reports. In many non-pharmac ological randomized clinical trials, the subjects cannot be blinded to treatment. Furthermore, many of them will probably have a preference for a particular treatment option. It has been proposed that emotional responses following assignment of treatments, which may or may not be preferred, will strongly influence the outcome, especially when it is based on self-reports of treatment satisfaction. Because of this conc ern, some investigators have suggested alternative study designs that incorporate preference. Brewin & Bradley (Br Med J 1989; 299 [6694]:31 3-5) have proposed allocating subjects to treatment methods according to their preferences, and randomizing those individuals with no prefer ence. To determine the influence of preference on treatment outcome, t hey recommend comparing results from the preference group with those o f the randomized group. However, we have found that there are dear dif ferences in level of education and in the pre-treatment state between individuals with preferences and those with no strong preferences. The refore, we believe that the design proposed by Wennberg et al. (Ann N Y Acad Sci 1993;703:52-62) is more appropriate. Ln it, subjects are ra ndomly allocated to a preference trial (subjects choose their treatmen t) or to a randomized trial (random allocation to treatment). Between- trial comparisons can then be used to determine the influence of prefe rence on outcome. This will lead to better evaluation of treatment eff icacy and allow better estimates of the true effectiveness to be made.