Jolly et al. BMC Public Health 2010, 10:439 http://www.biomedcentral.com/1471-2458/10/439 presence or absence of co-morbidities. The threshold for invitation for people with no obesity-related comorbidity is a BMI of ≥ 30 Kg/m2 in any ethnic group except South Asian and BMI ≥25 Kg/m2 in South Asians. For people with obesity related comorbidity the threshold for invita- tion is a BMI ≥ 28 Kg/m2 for all ethnicities apart from South Asians, for whom it is BMI ≥ 23 Kg/m2. Their GP has to confirm that they have no medical contra-indications for any of the intervention pro- grammes. Patients are excluded if they are unable to understand English, are pregnant or are unwilling to be randomised. Recruitment commenced in January 2009. Each gen- eral practice identifies eligible patients using a search of the computerised clinical record and invites them by standard letter to participate in the weight loss trial. Practices are asked to exclude patients with serious co- morbidities for whom weight loss programmes were unfeasible or inappropriate, for example those with terminal illness. The invitation letter contains informa- tion about the trial and a toll-free telephone number for a call centre managing the recruitment and randomisa- tion. The nurses at the call centre provide more infor- mation to patients about the trial, answer questions, collect baseline information, take verbal consent and randomise patients to the trial arms. The call centre books participants into their first treatment session and sends confirmation, along with verification of consent and information on how to withdraw from the trial if they change their minds. Participants allocated to the general practice, pharmacy or minimal exercise interven- tion (comparator) arms are sent details about how to arrange their first session. The randomisation sequence was prepared by an inde- pendent statistician and to ensure blinding, each alloca- tion was placed in an opaque, consecutively numbered envelope. These are used in order by the call centre staff, who record the number of the envelope and time of randomisation to enable the study team to check these are used in the correct order. Following the first programme session, the call centre telephones the participants to check whether they attended and rebook appointments if necessary. If parti- cipants have not attended and have no wish to do so, nurses record the reasons for this. Interventions The content and delivery of the interventions are described in the Table 1. In addition the interventions have been classified according to Abraham and Michie’s taxonomy of behaviour change techniques [19] by extracting the elements of the interventions from written manuals and materials provided by the programmes. Page 3 of 8 The participants allocated to the commercial operators Weight Watchers [20], Slimming World [21] and Rosemary Conley [22] have a choice of programme loca- tions and times. Commercially, these programmes run continuously, with no set number of sessions and no fixed starting date. People who are not participating in the trial pay fees to attend these programmes and these people attend alongside those in the trial, for whom treatment is free. Each programme is provided in accor- dance with the respective organisations’ guidance and the group leaders are trained by the organisations. The vouchers provided to trial participants exempts them from payments for the first 12 weeks of the programme. Thereafter, if participants wish to continue attending sessions they are required to pay the appropriate fees to the service provider. The Size Down Programme is an NHS group-based programme in which all members of the group commence together and follow a prescribed course of sessions. It takes place in various community venues. Participants randomised to the general practice or pharmacy arms attend one-to-one sessions in the general practice or pharmacy. Appointments are made at a time mutually convenient to the participant and the nurse/pharmacist. In the choice arm, participants are able to choose from any of the intervention programmes described above. Participants allocated to the comparator group are sent vouchers for 12 free sessions to attend a local authority run leisure centre (typically including an exer- cise room, swimming pool, and other facilities such as squash or badminton courts). Participants are not given an appointment to attend and are given no dietary or individual physical activity advice and support. It is acknowledged that weight loss can occur with exercise- only, but effects are modest [8,23]. Data collection Baseline data Data collected at baseline by the call centre, prior to randomisation includes: demographic data, information on previous use of weight loss programmes including commercial services, current physical activity levels (using the International Physical Activity Questionnaire- short form (IPAQ-short)) [24] and use of weight loss medication. Patients allocated to the choice arm are asked about their reasons for choosing their programme. When participants attend their first weight-loss ses- sion in the six interventions, the leader/counsellor mea- sures participants’ height and weight. Scales are validated by the research team using standardised weights, unless evidence of recent independent valida- tion is provided. The commercial providers often use self-reported height, so this will be re-measured at