Int. J. Environ. Res. Public Health 2010, 7 2794 interest that had not relapsed at each observation time. A sharp decrease of the function at a specific time indicates that a large number of individuals relapsed at that time. We clearly see that the survival function for individuals with only a compulsory education is lower than the function associated with more highly educated individuals, indicating a higher relapse rate among less educated individuals. The same relationship was observed between high and low income individuals. Figure 1. Non-parametric survival functions by education and income. 3.3. Multivariate Analysis 3.3.1. Successful Cessation Analysis Estimation results are shown in Table 2. We observed an important socioeconomic gradient in successful cessation with respect to both education level and income. In the group with higher education, the odds of being a successful quitter in comparison with the reference category (compulsory education) reached 1.39 for men and 1.78 for women. The influence of higher income levels is comparable in size for both subgroups (ORmen = 1.65 and ORwomen = 1.47). We observed that the odds of being a successful quitter were linked with marital status for both men and women (ORmen = 1.36 and ORwomen = 1.36). Table 2. Successful cessation—Multivariate logistic regressions. Education Compulsory Secondary Higher Odds of successfully quitting Men Women 1.00 (ref.) 1.13 (0.92) 1.39* (2.15) 1.00 (ref.) 1.40** (3.10) 1.78*** (4.49)