Correlates and confounding factors

Studies I and II

The variables for correlates of substance use disorders, used in studies I–IV are listed in Table 4. Studies I and II included a range of correlates, selected on the basis of earlier studies on risk factors for substance use disorders and categorized as representing the four domains of behavioral and affective factors, parental factors, early initiation of substance use, and educational factors. In Study I, the relative contributions of these factors as correlates of substance use disorders were studied, whereas they were included as covariates in the analyses of cognitive functioning in Study II. In addition, comorbid psychiatric diagnoses based on the best-estimate diagnostic procedure were used as covariates in Study II.

TABLE 4. Correlates of substance use disorders included in studies I–IV.

Studies I & II Study III Study IV

Domain Variable Data source Variable Data source Variable Data source

Education &

MEAF: the Mental Health in Early Adulthood in Finland study; FT16: the FinnTwin16 study; SSAGA: the Semi-Structured Assessment for Genetics of Alcoholism; DSM-IV: The Diagnostic and Statistical Manual of Mental Disorders, 4^th Edition;

SCID-I: the Research Version of the Structured Clinical Interview for DSM-IV; DSM-III-R: The Diagnostic and Statistical Manual of Mental Disorders, 3rd Edition, Revised

Behavioral and affective factors included the following variables. Attention or behavior problems at school were derived from a set of questions on difficulties during school time, lasting longer than one semester (four to five months). A positive response to either of the items on attention or behavior problems was used as an indicator of attention or behavior problems at school. Aggression was assessed with a short measure of trait aggressiveness, constructed based on selected items from the Buss-Perry Aggression Questionnaire (Buss and Perry 1992). Two items from each of the four aggression subscales were translated into Finnish, creating an eight-item scale. A summary scale of the eight items, responded to on a five-point Likert scale, was constructed (theoretical range 8-40, coefficient alpha = .82). Aggression scores were further classified as low (<11), moderate (11–17), and high (>17), approximating the observed 25^th and 75^th percentiles. Anxiousness was assessed with a single item that has been used as an indicator of trait anxiousness

in previous studies in Finland (Fröjd et al. 2007). The question asked was “Are you usually tense or distressed”. The five-point scale was: 1 “I have good control over my feelings and do not become tense or distressed easily”, 2 “I do not feel tense or distressed”, 3 “I become distressed quite easily”, 4 “I become anxious, tense or distressed very easily”, and 5 “I feel anxious or tense all the time as if I had lost my nerves”. A three-class variable was created by classifying anxiousness scores 1 and 2 as low, score 3 as moderate, and scores 4 and 5 as high.

Parental factors included parental alcohol problems, derived from a series of questions concerning various childhood adversities, experienced before age 16.

Items “Did your father have alcohol problems” and “Did your mother have alcohol problems” were combined so that a positive response to either item was considered as an indicator of parental alcohol problems. Parental basic education was also included, such that a binary variable of having at least some academic secondary (high school) studies vs. not was created on the basis of the highest secondary education of either parent.

Factors related to substance use initiation were age at initiation of daily smoking and age at initiation of drinking to intoxication. Lifetime never-smokers were classified as a separate category, while for smokers the age at daily smoking initiation was categorized into three classes: 18 years or older, 15–17 years, and younger than 15 years. Concerning drinking to intoxication, the question “At which age were you for the first time so drunk that you felt sick afterwards?” was asked. Three classes were created: those responding “Never” or at age 18 or older, at age 15–17, and at age younger than 15 years.

Educational factors included learning difficulties at school and basic education.

Having had learning difficulties at school was determined as a positive response to any of the four learning related difficulties items (Reading, Writing, Mathematics, Languages) in a set of questions related to school time problems. For basic education, a binary variable was created coding academic secondary education (high school degree) and less than academic secondary education as separate categories. Basic education was included instead of highest attained education because a large part of the sample were still students.

Study III

Comorbid psychiatric diagnoses were available from the SSAGA interview. Other covariates included in Study III were basic education, using the same dichotomous classification as in Studies I and II, and age at initiation of daily smoking and drinking to intoxication, also categorized identically to Studies I and II.

Study IV

In Study IV, the focus was on the relationship between alcohol problems and educational level. Information on the attained level of education was available as categorical classifications of each participant’s completed and ongoing studies. Using this information, a variable representing the estimated total years of education was

created. This was done on the basis of the standard duration of each type of education.

In the Finnish educational system, compulsory education continues through grade nine (age 16). Secondary education is divided into vocational (non-academic) and academic secondary education (high-school), which typically take two and three years to complete, respectively. Tertiary education is provided by polytechnics and universities, lasting typically three and a half and five years, respectively. Polytechnics train professionals in various fields in response to labor market needs, whereas universities conduct scientific research and provide the highest levels of education.

In order to enter tertiary education, academic secondary education is generally required, although some exceptions exist. For the participants who still had their studies underway when completing the young adult questionnaire, ongoing studies were taken into account by using half of the standard duration of the type of education in question as an average estimate of years studied. For example, individuals who reported having completed academic secondary education and currently studying in the university were thus given the value 14.5 (9 + 3 + 2.5) for years of education.