Int. J. Environ. Res. Public Health 2010, 7 2797 Several shortcomings of our study should be noted. First, we pooled seven cross-sectional data sets and controlled for aggregate changes over time using year dummy variables. Each year a new random sample was drawn from the population, and the distributions of the variables probably changed over time. This could lead to biased estimates. Second, a large proportion of respondents did not provide any information about their income, significantly reducing our sample size. Third, we relied on self-reported information to determine smoking-related outcome variables, which are consequently likely to exhibit misreporting and recall bias. Although several studies confirm the reliability of self-reported smoking status (see e.g., Caraballo et al. [21]), we must interpret our results with caution, as we don’t know if this is the case with self-reported data on smoking cessation. Another important point is that the database fails to provide retrospective information about variables such as consumption level (number of cigarettes smoked per day) or dependence (Fagerström test for nicotine dependence) for former smokers. We were therefore unable to control for these potentially influential factors. In addition, information about smoking cessation therapies was not exploited because it was available only for two observation years. Finally, as mentioned by Piasecki et al. [22] in their article about relapse: “relapse to smoking is a dynamic process that may unfold idiosyncratically, and no single metric can perfectly summarise the relapse process.” The authors mention the problem of renewed attempts that are not taken into account in duration analyses of relapse, as was the case in our study. The policy implications of this study are important. We have shown that there is a socioeconomic gradient with respect to education and income in two outcomes associated with smoking cessation: the probability to quit successfully and the duration of abstinence. Lower success rates and shorter abstinence durations are apparent among lower socioeconomic groups in comparison with upper groups. The lag between smoking and its related diseases is important; and we may thus expect to observe an increasing prevalence of smoking-related disease among lower socioeconomic groups in the near future. Increasing cessation success rates and prolonging the duration of abstinence (with definitive abstinence as a final objective) in such disadvantaged groups could lead to an important reduction in smoking inequalities and a reduction of health inequalities in the longer term. Appropriate policies targeted at lower social classes have to be implemented. Available products aimed at improving cessation success can considerably enhance long-term abstinence rate [23,24]. However, they are expensive and are not reimbursed by the social health insurance programs available in Switzerland. To improve success rates and extend abstinence periods, smoking cessation therapies including nicotine replacement therapies, nicotine-free medications and counselling should be made more accessible to lower socioeconomic groups. References 1. 2. Lopez, A.; Collishaw, N.; Piha, T. A descriptive model of the cigarette epidemic in developed countries. Tob. Control 1994, 3, 242-247. Jha, P.; Peto, R.; Zatonski, W.; Boreham, J.; Jarvis, M.J.; Lopez, A.D. Social inequalities in male mortality, and in male mortality from smoking: Indirect estimation from national death rates in England and Wales, Poland, and North America. Lancet 2006, 368, 367-370.