Explanatory variables SITUATIONAL/ORGANISATIONAL FACTORS Recent treatment contact No Yes Referral route1 Non-criminal justice Criminal justice Area of residence (public health zone) Cheshire and Merseyside Cumbria and Lancashire Greater Manchester Deprivation 1 (most) 2 3 4 5 (least) PERSONAL CHARACTERISTICS Sex Female Male Age group (years) 18–24 25–34 35–44 45–54 55–74 Ethnicity2 White Mixed Asian/Asian British Black/Black British Other DRUG USE Opiate user No Yes Stimulant user No Yes Alcohol user No Yes 5476 (44.8%) 6754 (55.2%) 7801 (73.2%) 2854 (26.8%) 4702 (38.4%) 2942 (24.1%) 4586 (37.5%) 3465 (28.3%) 1800 (14.7%) 2268 (18.5%) 2979 (24.4%) 1718 (14.0%) 3359 (27.5%) 8871 (72.5%) 1902 (15.6%) 5487 (44.9%) 4071 (33.3%) 654 (5.3%) 116 (0.9%) 11343 (95.3%) 142 (1.2%) 209 (1.8%) 130 (1.1%) 76 (0.6%) 3530 (28.9%) 8700 (71.1%) 7087 (57.9%) 5143 (42.1%) 11254 (92.0%) 976 (8.0%) 809 (49.1%) 840 (50.9%) 1084 (74.6%) 370 (25.4%) 424 (25.7%) 438 (26.6%) 787 (47.7%) 364 (22.1%) 286 (17.3%) 328 (19.9%) 388 (23.5%) 283 (17.2%) 438 (26.6%) 1211 (73.4%) 362 (22.0%) 780 (47.3%) 436 (26.4%) 64 (3.9%) 7 (0.4%) 1462 (93.5%) 23 (1.5%) 53 (3.4%) 19 (1.2%) 7 (0.4%) 560 (34.0%) 1089 (66.0%) 961 (58.3%) 688 (41.7%) 1550 (94.0%) 99 (6.0%) BMC Public Health 2008, 8:149 http://www.biomedcentral.com/1471-2458/8/149 Table 3: Characteristics of those dropping out of, and retained in, drug treatment (N = 13879) Retained (controls) – n (%) Drop out (cases) – n (%) 1 N = 12109; for 354 individuals the data were missing and for a further 1416 'other' was recorded so it was not possible to identify whether or not the referring agency was a criminal justice service. 2 N = 13464 There was a significant interaction between age group and deprivation and the coefficients from the logistic regres- sion model were used to explore this further. Figure 1 shows that, for those aged 18 to 24 years, the odds of drop out for deprivation quintile five (least deprived) were 1.93 (95% confidence interval 1.41 to 2.64) the odds of drop out for deprivation quintile one (most deprived). A simi- lar, though smaller, effect was evident for the 25 to 34 age Page 6 of 11 (page number not for citation purposes)