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. @entity1 : 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, @entity1  =  50%). Response rates ranged between 81 and 90% of the population. MEASUREMENTS: Measures on substance use included smoking and @entity285 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 @entity8769 declined from 29.6 in 1997 to 3.6% in 2014 (linear trend:   (2) (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:   (2) (1)   =  1614.3, P  <  0.001). Primary prevention factors strengthened over time. For example, the mean score for parents knowing where their @entity1 are in the evenings rose from 2.44 in 1997 to 3.08 in 2014 (Ftrend(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 (Ftrend(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.

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

@entity1 :: ('9606', 'Species') :: ['children', 'PARTICIPANTS', 'boys'] @entity285 :: ('D000431', 'Chemical') :: ['alcohol'] @entity8769 :: ('MESH:D000435', 'Disease') :: ['drunkenness']
@entity285 :: (D000431,Chemical) :: ['alcohol']
