BMC Public Health 2008, 8:149 http://www.biomedcentral.com/1471-2458/8/149 Table 4: Factors affecting drop out from drug treatment, bivariate analyses (N = 13879) Table 5: Factors affecting drop out from drug treatment, multivariate analysis (N = 13464) Explanatory variables 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) 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 Opiate user No Yes Stimulant user No Yes Alcohol user No Yes Mantel-Haenszel odds ratio (95% confidence interval) Reference 0.84*** (0.76 – 0.93) Reference 0.93 (0.82 – 1.06) Reference 1.65*** (1.43 – 1.90) 1.90*** (1.68 – 2.16) Reference 1.51*** (1.28 – 1.78) 1.38*** (1.17 – 1.61) 1.24** (1.07 – 1.44) 1.57*** (1.33 – 1.85) Reference 1.05 (0.93 – 1.18) Reference 0.75*** (0.65 – 0.85) 0.56*** (0.48 – 0.65) 0.51*** (0.39 – 0.68) 0.32** (0.15 – 0.69) Reference 1.26 (0.81 – 1.96) 1.97*** (1.45 – 2.67) 1.13 (0.70 – 1.84) 0.71 (0.33 – 1.55) Reference 0.79*** (0.71 – 0.88) Reference 0.99 (0.89 – 1.09) Reference 0.74** (0.59 – 0.91) 1 N = 12109 individuals; 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 ** P ≤ 0.01, *** P ≤ 0.001 group. Conversely, for those aged 55 to 74 years, the odds of drop out for deprivation quintile five were 0.37 (95% confidence interval 0.18 to 0.73) the odds of drop out for those living in deprivation quintile one. A similar effect of smaller magnitude was observed for the 45 to 54 year age group. No interactions between age group and other explanatory variables were observed. Other explanatory Explanatory variables Ethnicity White Mixed Asian/Asian British Black/Black British Other Alcohol user No Yes Area of residence (public health zone) Cheshire and Merseyside Cumbria and Lancashire Greater Manchester Deprivation 1 (most) 2 3 4 5 (least) Age group (years)1 Effect of interaction between age group and deprivation 1 (most) 2 3 4 5 (least) Adjusted odds ratio (95% confidence interval) Reference 1.14 (0.73 – 1.79) 1.52** (1.12 – 2.08) 1.10 (0.67 – 1.79) 0.69 (0.32 – 1.51) Reference 0.73** (0.59 – 0.91) Reference 1.80*** (1.51 – 2.15) 2.00*** (1.74 – 2.29) Reference 1.41 (0.85 – 2.34) 1.05 (0.65 – 1.70) 1.06 (0.67 – 1.70) 2.92*** (1.74 – 4.90) 0.88 (0.76 – 1.01) Reference 0.92 (0.75 – 1.14) 1.01 (0.83 – 1.24) 0.95 (0.78 – 1.15) 0.66*** (0.52 – 0.83) Other variables entered into the model: opiate use, recent treatment contact. 1 The effect of age group showed a linear trend; the adjusted odds ratio represents the common odds ratio across strata. ** P ≤ 0.01, *** P ≤ 0.001 Goodness of fit: Pearson's χ2 = 322.16, P = 0.009 variables (opiate use and recent treatment contact) were not significantly associated with treatment outcome fol- lowing simultaneous adjustments for other variables. The goodness of fit test suggested that the final model was not a good fit to the data (Pearson's χ2 = 322.16, P = 0.009). Discussion Retention in drug treatment is considered by the NTA to be the best available measure of treatment effectiveness [4]. To encourage a reduction in drop out rates, treatment retention measures were included in local partnership treatment plans and Primary Care Trust local delivery plans for the first time in 2004/05 [12], with 75% of drug users expected to be retained in treatment for at least 12 weeks during each annual reporting period [4]. Rates of retention can be improved by better understanding factors associated with premature drop out. The aims of the present study were to assess whether the retention target was achieved in the North West of England in 2005/06 Page 7 of 11 (page number not for citation purposes)