Ahern et al. BMC Public Health 2011, 11:434 http://www.biomedcentral.com/1471-2458/11/434 who were not prescribed a second course (t(22,517) = 37.8, p ≤ 0.001). Weight change by referral course number for an indi- vidual (’referral rank’) is illustrated in Figure 2. Weight loss per course decreased with increasing rank, although later courses did result in small additional weight loss. Median weight change for all first recorded referrals commenced (n = 22,519) was -3.6 kg (IQR -6.4 - -1.0 kg), which equates to -3.6% (IQR -6.7 - -1.1%) of base- line weight. 38% of commenced first referrals resulted in ≥5% weight loss (Figure 3). Analysis of those who completed all 12 sessions of a first recorded referral course (n = 11,851) showed that median weight change was -5.4 kg (IQR -7.8 - -3.1 kg), or -5.6% (IQR -8.1 - -3.2%) initial weight. 57% lost ≥5% and 12% lost ≥10% of initial weight (Figure 3). In participants completing a first referral course, med- ian percent weight loss was greater in men than women; greater in participants over 40 y than in younger partici- pants; and in those with a BMI between 30 and 40 kg/ m2, relative to BMI < 30 kg/m2, though the absolute dif- ferences were very small (Table 1). There was statisti- cally less weight lost as the period of time to complete the 12 sessions increased beyond the 12-week reference period, though absolute weight loss was greatest in the 5% of participants for whom final weight was recorded more than 24 weeks after baseline. Discussion This study examined weight loss in the WW NHS refer- ral scheme and found that a third of all commenced referrals resulted in weight loss of ≥5% initial body weight, which is expected to have clinical benefits [4]. In patients completing a first referral course, median No Return Repeat Referrals ) g k ( e g n a h C t h g i e W Referral Rank Figure 2 Median weight change (kg) and IQR of completers by recorded referral rank (outliers excluded from plot). % 0 5 itsanp 04% c i t r a P fgeo 30% a t n e c reP 0% 2 % 0 1 Page 3 of 5 Al referrals Completers > 10% Loss 5-9.9% Loss 0.1-4.9% Loss No Loss Gain Weight Change Figure 3 Percentage of initial weight lost for all first recorded referrals commenced and those completing a first referral course (as a percentage of participants). weight loss was 5.4 kg (5.6% initial weight), with more than half losing ≥5%. Weight loss in this programme is comparable to other studies of commercial or primary care-based weight loss programmes. For example, in the Counterweight pro- gramme 25.3% of participants lost ≥5% at 3 months, 40.2% at 6 months and 33.7% at twelve months [8]. Results are similar to a small pilot study of primary care referral to Slimming World, where participants complet- ing a 12 week course lost 5.4 kg, with 57% losing ≥5% baseline weight. In a randomised controlled trial of Table 1 Multivariate effects of covariates on median percent weight change for those completing a first referral course (median, p-value and 95% confidence interval) Percent Weight Change Median P value 95% CI Course Duration (weeks) 12 13-24 >24 Gender Female Male Age (years) < 40 40-49 50-59 60+ Start BMI <30 30-34 35-39 40+ N (%) 7,972 (67) 3,243 (27) 636 (5) 10,577 (89) 1,274 (11) 2,818 (24) 2,606 (22) 2,612 (22) 3,815 (32) 1,189 (10) 4,315 (36) 3,461 (29) 2,886 (24) - 0.70 -0.84 - -0.54 - -0.25 -0.34 -0.14 - -0.32 -0.04 0.38 - - < 0.001 (0.51, 0.89) < 0.001 (-1.21, -0.46) - - < 0.001 (-0.81, -0.27) - 0.051 0.007 0.237 - 0.035 0.775 0.018 - (0.49, 0.00) (-0.59, -0.09) (-0.36, 0.09) - (-0.62, -0.02) (-0.35, 0.26) (0.07, 0.70)