Jolly et al. BMC Public Health 2010, 10:439 http://www.biomedcentral.com/1471-2458/10/439 Page 6 of 8 Practices run searches for patients with raised BMI GPs screen list for patients with serious comorbidity Practice sends letter to overweight patients inviting them to free weight loss programme. Letter states that they will be required to provide PCT with data on their progress as the programmes are being evaluated. Patient information leaflet sent with the invitation letter. Free phone number for the call centre provided Interested patients telephone call centre Call centre explains that they will be randomly allocated to a programme after they have provided some details about themselves Patients give verbal consent. Baseline data collected over phone. Randomisation to one of 8 groups Commercial programme: Slimming World n=100 Pharmacy One-to-one programme n=70 General practice One-to-one programme n=70 Minimal intervention comparator n=100 Commercial programme: Weight Watchers n=100 Commercial programme: Rosemary Conley n=100 Size Down Group-based NHS community weight loss programme n=100 Choice Participants can choose any of 6 intervention programmes n=100 All programmes collect data on weight and physical activity at baseline (entry to programme) All programmes collect data on weight and physical activity at 3 months (end of programme) Research team collect data from those who have dropped out of their programme Blinded follow-up of all participants at 12 months 1 Figure 1 Patient flow through trial. BMI, participants are asked to complete the IPAQ- Short, their opinion of the service and whether they have tried any other weight loss programmes or strate- gies over the course of the year. Participants are invited to attend their general practice for a brief appointment, where the practice nurse or a health trainer who is blind to the allocation arm, undertake follow up mea- sures. Participants unable to attend their general prac- tice will be offered home visits for measurements. If height has not been measured previously, it is assessed using a Leicester height measure. Participant flow through the trial is shown in figure 1. Sample size A sample size calculation based on detecting a 2 kg difference in weight loss at the 12 week follow-up between any of the planned interventions and com- parator group, with 90% power and 5% significance level found that 70 participants randomised to each group will be sufficient. This estimate is based on a standard deviation of 3.2 kg [11,14] and allows for a 20% dropout rate. To enable a more realistic drop-out rate and to get greater precision, 100 participants were allocated to each arm. However, not many general practices or pharmacies were prepared to offer treat- ment themselves and training places were limited, so that only 70 will be allocated to these arms. A total of 740 participants will be randomized. Planned analysis Both between and within group analyses for primary and secondary outcomes at programme end and 12 months will be performed according to intention to treat. Participants in whom weight at follow up is not available will be assumed to have their baseline weight. However, sensitivity analysis will also be undertaken, assuming follow up weight to be the last recorded weight. As the outcomes are all measured on a continuous scale (weight loss, percentage weight loss, self-reported physical activity), differences between intervention group and the comparison (minimal intervention) group will be investigated using least squares linear regression. Between group analyses will be expressed as both unad- justed and adjusted differences (corrected for baseline score and covariates of age, gender, ethnicity and educa- tional level). A secondary analysis will compare the out- comes of the commercial weight loss programmes (Weight Watchers, Slimming World and Rosemary Con- ley) with the primary care programmes (general practice and pharmacy-based interventions). Data on choice of programme, number of sessions attended and reasons