Int. J. Environ. Res. Public Health 2010, 7 2791 behaviours. We investigated the following research questions: (1) Which aspects of social position are the strongest predictors of successful cessation? (2) Which socioeconomic factors influence the time before relapse? (3) Do the socioeconomic determinants of successful cessation and abstinence duration differ between men and women? 2. Method 2.1. Data We pooled data from the 2001–2007 editions of the Swiss Tobacco Monitoring Survey [14], a nationwide, cross-sectional survey of 14–65 year-olds conducted annually in Switzerland since 2001. Each quarter about 2,500 individuals are interviewed by phone in French, German or Italian, resulting in a total of about 10,000 observations per year (several subgroups of the population were oversampled—men aged 14–24, women aged 14–44 and individuals from the Italian and French linguistic regions). Combined, the seven cross-sections consisted of 70,216 respondents. In addition to demographic and socioeconomic information, the database contains a large number of variables related to smoking history and current smoking behaviour. From the base sample, we constructed one subsample which consisted of current and former smokers, aged 18 and over, who had recently attempted to quit. 2.2. Variables 2.2.1. Outcome Variables To distinguish between successful and unsuccessful quitters we had to exploit information about individual smoking history. We based the construction of this variable on the work of Lee and Kahende [12], who conducted a similar type of analysis in the United States. Unsuccessful quitters were defined as current smokers who had tried to quit at least once during the last 12 months, i.e., current smokers who answered yes to the question “Did you seriously try to quit smoking during the past 12 months?” Successful quitters were defined as ex-smokers who quit between seven and sixty months ago (our analysis focuses on recent cessation activity, which is the reason why we did not include individuals who quit more than five years ago). As suggested by Lee and Kahende [12], we excluded smokers who quit in the past six months because the risk of relapse is often very high for these people. The dependant variable in the relapse analysis was the duration in days of the longest quit attempt (also referred to as the duration of abstinence). Successful quitters were treated as censored observations since no relapse has been observed for them. 2.2.2. Independent Variables Demographic characteristics included age, gender and marital status. Age was categorised into three groups: 18–24, 25–44 and 45–65. Marital status was used to distinguish between married and non-married respondents. Socioeconomic variables included education level and household income. Education was divided into three categories as follows: basic education (no education or compulsory