Ahern et al. BMC Public Health 2011, 11:434 http://www.biomedcentral.com/1471-2458/11/434 programme (4.3 ± 6.1 kg vs. 1.3 ± 6.1 kg; p < .001) [7]. However, there is no published data on weight change fol- lowing referral to WW by a health professional, when the treatment package is funded by the Primary Care Trust (PCT) at no cost to the patient. Such information is vital to inform evidence-based commissioning of weight man- agement services. Methods Study Design The aim of this observational study was a retrospective examination of weight change in NHS patients referred and funded by their primary care provider to 12 sessions of WW, at a cost of £45 per participant. Data were obtained from the WW NHS Referral Scheme database for all referral courses started after 2nd April 2007 (when WW began recording objective weights for all com- menced referrals) and ending before 6th October 2009, and were analysed by an independent research team. Participants The complete dataset contained 29,560 referral courses in which the patient commenced the referral by attend- ing at least one WW meeting. No data was available on the total number of patients who were referred but did not attend any sessions. Referrals were excluded if there was no recorded height, gender was unknown, or if there were discrepancies between course completion, defined by WW, and number of meetings attended. Data from 29,326 referral courses (99%) were included in the final analyses. Measurements The initial weight of participants was measured and recorded by WW leaders and relayed to the central database by telephone or email. Body weight was mea- sured at each subsequent session by WW leaders and the final body weight was similarly relayed to the data base when patients either lapsed (defined as no atten- dance or communication from a participant for a 5 week period) or completed 12 sessions. Statistical Analysis Statistical analyses were conducted using Stata/IC 10.1 software. Data were not normally distributed so medians and inter-quartile ranges (IQR) were used to represent the data. Data were analysed for all referrals attending a first meeting and for participants completing all 12 ses- sions of a first referral course during the audit period (completers only analysis). These analyses assumed there was no weight change for participants who attended only one session. A multiple linear regression model was used to analyse the effect of covariates on percent weight change. Page 2 of 5 Ethics This study was an audit. No data was collected outside of routine clinical care and all databases were anonymised. All individuals referred to WW as part of the NHS refer- ral scheme gave consent to their data being audited. Results Baseline characteristics of referrals Of the 29,326 referrals, 26,252 (90%) were female. Med- ian age was 49 years (IQR 38 - 61 years). Median weight at the start of the referral course was 94.3 kg (IQR 83.7 - 107.7 kg) and median start BMI was 35.1 kg/m2 (IQR 31.8 - 39.5 kg/m2). Attendance Attendance for the 29,326 referral courses is shown in Figure 1. 1,570 (5%) of participants attended only 1 ses- sion and 15,885 (54%) attended all 12 sessions. Among completers, the median duration of attendance was 12 weeks (IQR 12 - 14 weeks). Weight change Median weight change for all commenced referrals was -2.8 kg (IQR -5.9 - -0.7 kg), which equates to -3.1% (IQR -6.1 - -0.7%) of baseline weight. 33% of referrals resulted in ≥5% weight loss. Median weight loss increased as number of meetings attended increased, (p-trend ≤ 0.001; Figure 1). Some courses were repeat referrals for the same patient. 11,851 (75%) of the completed 15,885 courses were the first recorded referral for an individual during the recording period. 3,088 (19%) represented a second referral and 729 (5%) a third. The remaining 217 (1%) were the fourth to eighth courses prescribed to an indi- vidual. Individuals later prescribed at least one repeat course lost more weight on their first course than those ) g k ( e g n a h c t h g i e W Number of sessions attended Figure 1 Median and IQR of weight change (kg) for all referrals by number of sessions attended.