Population trends in smoking, alcohol use and primary prevention variables among adolescents in Iceland, 1997-2014

Aims: To estimate linear time-trends in substance use and primary prevention variables in adolescents in Iceland from 1997 to 2014. Design: Repeated, cross-sectional population-based school surveys with seven waves of pooled data. Setting: Iceland. Participants: All accessible students enrolled in the 9th and 10th grades in the national Icelandic school system during the spring of 1997, 2000, 2003, 2006, 2009, 2012 and 2014 (n = 50 412, boys = 50%). Response rates ranged between 81 and 90% of the population. Measurements: Measures on substance use included smoking and alcohol use. Primary prevention measures included parental monitoring, parental social involvement, participation in organized sports and reduced participation in a party life-style. Findings: Substance use decreased consistently during the study period. For example, 30-day drunkenness declined from 29.6 in 1997 to 3.6% in 2014 (linear trend: χ²₍₁₎ = 2846.8, P < 0.001), and daily smoking during the last 30 days declined from 17.0 to 1.6% during the same period (linear trend: χ²₍₁₎ = 1614.3, P < 0.001). Primary prevention factors strengthened over time. For example, the mean score for parents knowing where their children are in the evenings rose from 2.44 in 1997 to 3.08 in 2014 (F_{trend(1, 42635)}, 2538.3, P < 0.001), and mean scores for participation in party life-style declined from 2.23 in 1997 to 1.71 in 2014 (F_{trend(1, 38773)}, 2033.1, P < .001). Conclusions: Substance use among adolescents in Iceland has declined steadily from 1997 to 2014, while primary prevention factors for substance use have increased in strength during the same time-period.