Design and Participants
An initial cross-sectional sample of 39,399 adolescents aged 12–19 years was invited to participate anonymously and voluntarily in the Life and Health Young Cross-sectional Survey (LHS), commissioned by the Uppsala County Council, Sweden to be conducted in schools in separate cohorts in 2005, 2007, 2009, and 2011. All respondents were asked to complete the survey once in one of these years, during school hours. In 2005 and 2007, data on age, household structure and drug use were not available, and so only years 2009 and 2011 were included in the current study. As such, a total of 9,667 adolescents were initially eligible for the present analysis. From this total, a further 99 adolescents were excluded for not having all data for age, gender and PSC, leaving a total of 9,568. Secondary exclusions of 6,436 participants were due to at least one missing answer on questions contributing to the total conduct problems score that was determined by related DSM-5 CD criteria (described below), leaving a total of 3,132 for the main analyses. The flowchart of the study population exclusions is shown in Fig. 1. The data analysis was approved by the Ethical Committee of Uppsala (EPN).
Demographic data. Age, gender, living location (urban or rural), ethnicity (Swedish, Nordic, Other European, Outside Europe), people with whom the adolescents were living, type of living place, and parents’ employment, were recorded in the LHS.
Self-reported conduct problems. Conduct problem scores were created by summing scores for questions with Likert-scale or yes/no questions that two independent researchers linked to DSM-5 CD criteria, as summarised in Table 1. Thus, higher conduct problem scores were indicative of higher levels of behaviours typically associated with a diagnosis of CD. Inclusion of questions from the LHS for each CD criteria was checked and agreed independently by two researchers (SB and SBA). Details of each of the included LHS questions (with reference numbers) and their scoring (some scores were reversed by the authors to ensure that high scores reflect high level of conduct problems, as shown by the reference ‘R’) are given in Table 2.
DSM-5 CD criterion: Aggression to people or animals. 11 questions were selected from the total LHS to closely represent this criterion, with a cumulative minimum score of 11 and a maximum score of 49 (based on their Likert Score values, see Table 2), including questions such as: Have you exposed someone else to bullying, threats or harassment via mobile or SMS? Have you beaten, kicked or exposed someone else to violence during the school term? Have you participated in fights at school? Have you illegally carried a knife or other weapon in school? Answers included: No, One Time, Many Times, and Never, or One Time, 2–4 times, 5–10 times, more than 10 times.
DSM-5 CD criterion: Destruction of property. Only 2 questions from the LHS were closely matched to this criterion, with a cumulative minimum score of 2 and a maximum of 10 and included the questions: Have you deliberately destroyed or been involved in destroying things? And, have you been involved in scribbling, graffiti painting or writing something with a marker or spray paint without permission? Answers included: Never, one time, 2–4 times, 5–10 times or more than 10 times.
DSM-5 CD criterion: Deceitfulness or theft. 9 questions from the LHS closely matched this criterion, with a cumulative minimum score of 9 and maximum of 45, and included the questions: Have you taken money from home or a schoolmate? Have you been involved in a burglary? Have you stolen a bike, or a car? Answers included: Never, one time, 2–4 times, 5–10 times or more than 10 times.
DSM-5 CD criterion: Serious violations of rules. 10 questions from the LHS closely matched this criterion, with a cumulative minimum score of 10 and a maximum of 41, and included questions such as: How easy is it for you at home to say where you go? And, are you truant from school? And, have you not attended some of your subjects? Answers included: Many times, sometimes, not so many times, never. Or, No, not in any subject, Yes 1–2 subjects, Yes, 3–4 subjects, Yes, more than 5 subjects.
Total conduct problems score. All 32 questions from the categories above were summed to create a cumulative LHS minimum score of 32 and a maximum score of 145 (according to the Likert Scale scores for each question). Percentages for total LHS scores and the 4 categories (e.g. according to the highest possible score) were calculated for contrast homogeneity.
Assessment of self-reported psychosomatic complaints (PSC). 12 LHS questions related to psychological and 12 related to somatic (physical) complaints, which were again checked by the same two independent researchers (SB, SBA). Percentages for PSC total and subscale scores (e.g. according to the highest possible score for total Likert Scale scores) were calculated for contrast homogeneity. Three levels of PSC: low, medium and high were calculated as tertile thresholds of the total PSC percentage scores. See Table 3 for details of each of the included questions and their scoring (some scores are reversed to ensure that high scores denote high level of PSC).
Psychological complaints. The 12 psychological LHS questions have a cumulative minimum score of 12 and a maximum score of 53 and are related to: stress, nervousness, anxiety/worry, depression, happiness, medication for anxiety/depression/sleep disorder, reading/writing difficulties, neuropsychiatric disorder (e.g. ADHD), worries about sleep, occurrence of nightmares, and how bright the future looks. Answers include: Never, rarely, sometimes, often, always.
Somatic complaints. The 12 somatic (physical) LHS questions have a cumulative minimum score of 12 and a maximum score of 123 and are related to: how the person feels, incidence of migraine, headache, stomach ache, ringing in the ears/tinnitus, tiredness, pain in the neck and shoulders, pain in the back and hips, pain in the hands, knees, legs or feet, quality of dental health, whether prescription or non-prescription drugs are taking for headaches or other pain, hearing loss, visual impairment that cannot be correct with glasses, physical disability, difficulty sleeping, and whether the person is often tired. Answers include: never, rarely, sometimes, often and always. Total PSC score. All 24 LHS questions above were summed to create a cumulative minimum score of 24 and a maximum score of 176, which allowed for the calculation of individual total percentage PSC scores.
SPSS version 25.0 (IBM Corp, 2017) was used. Descriptive statistics of the demographic data were conducted with t-tests for mean differences and chi-squared for frequencies, where applicable. Bonferroni correction was applied to control for multiple comparisons, and parametric assumptions (normal distribution, homogeneity of variance, sphericity and collinearity) were checked and data corrected if these assumptions were violated. A p-value of equal to or less than 0.05 denoted significant effects.
Analysis of variance (ANOVA) of total conduct problems score (n = 3,132). A 3-way independent measures design, incorporating the between-subject factors: age (dichotomised above and below the mean age of 16 years), gender (boys, girls) and PSC severity score (tertiles for low, medium, high) was utilised to examine main effects and interactions associated with variance in the total LHS conduct problem score.
Multivariate analysis of variance (MANOVA) of the 4 categories of conduct problems (n = 3,132). A 3-way independent measures design, incorporating the between-subject factors as above, was utilised to examine the main effects and interactions associated with score variance in the four conduct problem categories that were linked to DSM-5 CD namely: a) aggression to people/animals, b) deceit/theft, c) destruction of property, and d) serious violations of rules.