Re: Comparison of range of commercial or primary care led weight reduction programmes with minimal intervention control for weight loss in obesity: Lighten Up randomised controlled trial
We read with interest Jolly and others’ randomised controlled trial of the effectiveness of various weight-management programmes offered in primary care. In the study group, Weight Watchers achieved larger weight losses than other programmes. The study raises several questions about the interpretation of randomised controlled trial results when recruitment is low and patients demonstrate treatment preference. We have three interrelated observations to make on the interpretation of the results Jolly and others present.
The first is that low patient motivation and strong patient preference influenced participation in the trial. As the accompanying editorial highlights, the majority (88.5%) of eligible patients did not elect to participate in the trial. The absence of these patients leads to bias and restricts the generalisation of the study’s findings. The reported proportions of patients who achieved clinically significant weight losses at one year (for example, 31.0% at Weight Watchers) might therefore represent 3.6% of all patients that a GP referred for such weight management.
The second is that selection biases for trial participants may have led to an unrepresentative sample. Attendance is one of the major predictors of successful weight loss within weight management programmes and patients who attend programmes are not the same as those who drop out. It is unclear what selection biases might have affected the final study population but it seems reasonable to suggest that trial participants were not typical of the sampling frame. Participants may have been motivated by the possibility of obtaining free access to a commercial weight management programme and experienced “resentful demoralization” when offered NHS services.
The third is that the conclusions of the analysis of the effects of patient choice are unsound because there were insufficient numbers of patients (only 3 patients chose general practice for example) with which to draw informative conclusions. We feel that the authors’ conclusions, repeated in the Abstract without reference to the small number of patients, is misleading. It is not surprising that interactions between choice and programme were not found to be statistically significant, but it would have been helpful to have seen what they were. In open randomised trials, patients’ treatment preferences should be ascertained prior to randomisation.
 Jolly K, Lewis A, Beach J, Denley J, Adab P, Deeks J and others. Comparison of range of commercial or primary care led weight reduction programmes with minimal intervention control for weight loss in obesity: Lighten Up randomised controlled trial. BMJ 2011;343:d6500 doi: 10.1136/bmj.d6500
 Truby H. What makes a weight loss programme successful? BMJ 2011;343:d6629
 Honas JJ, Early JL, Frederickson DD, O’Brien MS. Predictors of attrition in a large clinic-based weight-loss program. Obesity 2003;11:888-894.
 Bradley C. Designing medical and educational intervention studies. Diabetes Care 1993;16:509–18.
 Preference Collaborative Review Group. Patients’ preferences within randomised trials: systematic review and patient level meta-analysis. BMJ 2008; 337 doi: 10.1136/bmj.a1864.
Competing interests: We have evaluated the Counterweight programme and other providers’ weight management programmes but we have no financial interests in the Counterweight Company or any others.