Randomised controlled trials: missing data

Researchers assessed the effectiveness of a range of weight management programmes for weight loss. A randomised controlled trial study design, incorporating eight treatment arms, was used. Each intervention—Weight Watchers, Slimming World, Rosemary Conley, a group based dietetics led programme, general practice one to one counselling, pharmacy led one to one counselling, and a choice of any of the six programmes—lasted for 12 weeks. The control treatment consisted of 12 vouchers enabling free entrance to a local leisure (fitness) centre. Participants were 740 obese or overweight men and women identified from general practice records.1

The primary outcome was weight loss at the end of the programme (12 weeks). Secondary outcomes included weight loss at one year. Baseline characteristics were available for all participants, whereas follow-up data were available for 658 (88.9%) participants at the end of the programme and 522 (70.5%) at one year.

Analyses were performed according to intention to treat, using “baseline observation carried forward” to account for missing data. All treatment programmes achieved significant weight loss from baseline to programme end. When compared with the control treatment at 12 weeks, the only programmes that resulted in significantly more weight loss were Weight Watchers (mean difference 2.53 kg, 95% confidence interval 1.30 to 3.76; P<0.001) and Rosemary Conley (2.18, 0.96 to 3.41; P=0.004). All programmes except general practice and pharmacy provision resulted in significant weight loss at one year. At one year, only the Weight Watchers programme resulted in significantly …