Study population and setting
The current cross-sectional study was conducted in Switzerland as part of the Cohort Study on Substance Use Risk Factors (C-SURF) [17, 18]. The participants in this large study are young Swiss men who were approached and recruited during the mandatory two-day assessment procedure to determine eligibility for military service. Because it is mandatory, virtually all males at age 19 must attend one of the recruitment centers, thus providing a unique opportunity to access a large representative sample of the general population of young men in Switzerland. Recruitment for C-SURF took place at three of the six army centers, one in the French-speaking sector (Lausanne) and two in the German-speaking sectors (Windisch and Mels). These three centers are in charge of assessing the eligibility for Swiss military service in 21 of the 26 cantons of Switzerland.
Although women are allowed to voluntarily join the military service, most do not, thus they would not represent the general population and were excluded from C-SURF. Because substance use may influence eligibility in the army, there is some risk of under- or over-reporting substance abuse among attendees of the recruitment centers. Therefore all potential research participants were assured that any and all information gathered as part of the study was to be kept confidential from the army, and could not affect conscription procedures. Strong efforts were made to ensure that participants understood that the research was entirely independent of the army, which in no way could gain access to data connected to any individual.
All conscripts attending the centers were eligible for participation in C-SURF, provided they furnished written informed consent. Research staff informed potential participants (conscripts) that the study was a longitudinal survey. The goal of the study, studying substance use risk factors, was made clear to potential participants. Potential participants were also informed on the study procedures and the right to withdraw from the study at any time without penalty. Participants completed informed consent at the study recruitment site (army recruitment centers). The study questionnaires were completed by the participants after they left the army recruitment centers. The study was approved by the Ethics Committee for Clinical Research at the Lausanne University Medical School (protocol number 15/07).
Recruitment for this study took place between August, 2010 and November, 2011, during which time 13,245 center attendees were offered participation. Conscripts have the option of attending the recruitment centers while younger than 19, explaining some variation in age ranges observed in other studies conducted by our group at the army recruitment centers [19–21]. The 7,563 conscripts who were willing to participate received research questionnaires after leaving the recruitment centers, either in paper-pencil or online form, according to their preference.
Alcohol use in the past 12 months was assessed with drinking frequency and quantity questions: ”How often do you usually drink alcohol?” (participants were offered a range of response options: 7, 6, 5, 4, 3, 2, 1 day(s) a week; 2–3 times a month; once a month or less; never) and, “How many standard drinks do you drink on average on days when you drink alcohol?”(open question) . A standard drink was defined as 100 ml of wine, 250 ml of beer, 275 ml of a premixed drink containing spirits or 20 ml of spirits (each ∼ 10 g of ethanol), which is the commonly used definition of a standard drink in Switzerland . The questionnaire included visual aids with pictures of standard drinks and labels so as to identify various container sizes.
The frequency of risky single occasion drinking (RSOD), defined as 6 or more drinks per occasion, was assessed with the following question: “How many times have you had 6 or more standard drinks with alcohol, during the same occasion” (Participants were offered a range of response options: every day or nearly every day; every week; every month; less than once a month, never). The time reference was the past 12 months . Participants were later grouped into two categories: presence of monthly RSOD (every day or nearly every day, every week, every month) or absence of monthly RSOD (less than once a month, never). In Switzerland, six drinks contain ∼ 60 g of pure alcohol and is equivalent to the commonly used US measure of 5+ drinks of 12 g per drink . Our definition of RSOD is equivalent to the definition of NIAAA as well as to European standards.
Four dependent variables reflecting alcohol use over the past 12 months were used: 1) Any alcohol use over the past 12 months; 2) Presence of monthly RSOD; 3) Presence of weekly risky drinking (defined as 21 standard drinks per week or more); and 4) Weekly average consumption (mean number of standard drinks per week).
The weekly risky drinking definition used in the present study approximates the World Health Organization and other European clinical guidelines of risky drinking and the US National Institute on Alcohol Abuse and Alcoholism definition [18, 21, 23].
Tobacco use was measured as any cigarette use during the past 12 months through a yes or no question (“Have you smoked cigarettes in the past 12 months?”), as well as the frequency of smoking, through the question “How often have you generally smoked cigarettes in the past 12 months?”(Participants were offered a range of 6 response options, from “every day” to “once in a month or less”). Participants were later grouped into two categories: daily use, or less. Thus, the two tobacco measures used as dependent variables were any use over the past 12 months and daily tobacco use.
Cannabis use was assessed with questions included in the Cannabis Use Disorders Identification Test . We identified participants reporting any use over the past 12 months and differentiated those who consumed once a week or less from those who consumed more than once a week using the following questions: “Have you used any cannabis over the past 12 months?”(yes or no question) and, “How often have you used cannabis over the past 12 months?”(with 5 response options from “monthly or less” to “every day or almost every day”).
Other illicit drug use
Participants were asked about their use over the past 12 months use of the following substances: ecstasy; cocaine; heroin; and magic mushrooms through the question “Have you ever taken any of these drugs in the past 12 months? If yes, how often?”(with 3 response options “never”, “1 to 3 times” and “4 times or more”).
Non-medical use of prescription drugs (NMPD)
Participants were asked about their use on any day over the last 12 months of sleeping pills, tranquilizers, painkillers, stimulants, antidepressants, and beta blockers (“Now we would like to ask you about your experience with prescribed medicine in the last 12 months that you may have decided to use of your own will-that is, either without a doctor’s prescription or without a doctor telling you to use them. People use the following medicine or drugs of their own will to feel more alert, to relax or calm down, to feel better, to enjoy themselves, or to get high or just to see how they would work. Have you taken such medicine of your own will?”). Participants were offered 8 response options, varying from “never” to “4 times a week or more”.
Socioeconomic status (SES) indicators
We used three indicators of participant SES: perceived family income, own education level, and parental education level. Perceived family income was assessed because there is growing evidence that subjective economic power is a better predictor of health outcomes than objective economic power [27–29]. Hence, participants were asked to report their perception of their family income (“How well off is your family compared to other families in your country?”). Participants were grouped in two categories: average or below average, and above average. Participant education level was determined as the highest education level achieved by the participants at the time of assessment, characterized as having received obligatory or elementary vocational education only or having received more than that. Parental education level was assessed by asking participants to report the highest education level achieved by their parents (either father or mother) (“What is the highest level of education your parents achieved?”). Parental education level was categorized into obligatory, secondary (vocational training or school) or tertiary (university or university of applied sciences).
Relationships between SES indicators and substance use were first assessed using chi-square tests except for number of drinks/week for which analysis of variance testing equality of means was used. Subsequently, linear and logistic regression models adjusted for age, living environment (rural, i.e. < 10000 inhabitants vs. urban, i.e. ≥ 10000 inhabitants) and linguistic region (German—vs. French-speaking) were fit. In our sample, the age range was 17.9–27.8. In Switzerland, the legal age for purchase of beer and wine is 16, and 18 for hard liquors. For tobacco, the legal age for purchase varies by Canton (from no restriction to 18 years old, with most Cantons having a 16 or 18 year old legal age). Cannabis is an illegal drug in Switzerland (as the other drugs studied). Substance use is known to be associated with age. In addition, age can be associated with SES, notably the highest achieved education level. Analyses were therefore adjusted for age. Analyses were also adjusted for linguistic region and living environment since these can be associated with both SES indicators and substance use patterns. Substance use outcomes were first regressed on each SES indicators separately. Then, all SES indicators were tested simultaneously in a fully adjusted model. Finally, in order to test whether the associations of each SES indicators was moderated by other SES indicators, all two-way and three-way interactions between SES indicators were entered in the fully adjusted model. Since none of the interactions reached significance, results are not reported. In the regression models, SES indicators were contrasted as follows: average or below average vs. above average for perceived family income, obligatory or elementary vocational education only vs. more than obligatory or elementary vocational education for own education level, and tertiary vs. obligatory and secondary education for parental education level.
The dependent variables were any use of alcohol (past 12 months), prevalence of monthly risky single occasion drinking (RSOD), prevalence of weekly risky drinking, number of drinks per week, prevalence of tobacco use, cannabis use, other illicit drugs use (ecstasy, cocaine, heroin and mushrooms), as well as NMPD use (sleeping pills, tranquilizers, painkillers, stimulants, antidepressants, beta blockers).