Int. J. Environ. Res. Public Health 2010, 7 2793 (30.9%), 12,874 former smokers (20.3%) and 31,024 individuals who had never smoked (48.8%). The latter were excluded from the analysis, resulting in a base sample of 32,496 current or former smokers aged 18 and over. The successful cessation analysis compared the characteristics of former smokers who reported quitting seven to sixty months before the survey (N = 3,530) and those of unsuccessful quitters, defined as current smokers who had attempted to quit during the last twelve months (N = 4,145). For each analysis, our sample was limited to respondents who had no missing values for the relevant covariates, leaving 6,290 individuals for the cessation analysis (1,385 missing) and 6,136 individuals for the relapse analysis (1,539 missing). The majority of missing values were due to a lack of information about income. 3.2. Descriptive Analysis 3.2.1. Successful Cessation Analysis Both socioeconomic indicators were strongly associated with successful cessation (Table 1). The proportion of successful quitters was much higher among highly educated individuals than among respondents who had only completed compulsory education. We observed similar differences between the two extreme income groups. Table 1. Descriptive analysis of outcomes across socioeconomic subgroups. Cessation analysis (N = 6,290) absolute diff. in mean duration, absolute diff. the proportion relative diff. in days, of in mean % of of successful compared to longest quit duration successful quitters reference attempt compared to quitters compared to category (%) (unsuccessful reference reference quitters) category category (pp.) Abstinence duration analysis (N = 3,209) Education Level Compulsory 34.5 Secondary 45.4 Higher 54.2 Household Income Up to 4,000 39.6 4,000–8,000 47.5 8,000 + 53.9 - +10.9 +19.7 - +7.9 +14.3 - +31.6 +57.1 - +19.9 +36.1 61.8 86.6 99.4 79.4 87.1 100.5 - +24.8 +37.6 - +7.7 +21.1 3.2.2. Abstinence Duration (Relapse Analysis) In Table 1, we observe that, among unsuccessful quitters, the mean time before relapse was 60% higher for highly educated individuals in comparison with individuals who had only completed compulsory education. The duration was 25% higher for the highest income group in comparison with the lowest income group. Figure 1 shows the non-parametric estimates of the survival functions [19] with respect to both socioeconomic indicators. The data indicate the proportion of the population of relative diff. compared to reference category (%) - +40.1 +60.8 - +9.7 +26.6