Decrease in household secondhand smoking among Korean adolescents associated with smoke-free policies: grade-period-cohort and interrupted time series analyses

OBJECTIVES: Smoke -free areas have expanded and related campaigns have been implemented since 1995 in Korea. As a result, household secondhand smoke (SHS) exposure has decreased over the past 15 years. We assessed the cohort effect, the effect of a 2008 campaign on household SHS exposure, and the impact of a complete smoking ban in public places along with increased penalties, as implemented in December 2011. METHODS: Nationally representative cross-sectional 15 -wave survey data of Korean adolescents were used. The 810,516 participants were classified into 6 grade groups, 15 period groups, and 20 middle school admission cohorts. An age -period -cohort analysis, conducted with the intrinsic estimator method, was used to assess the cohort effect of household SHS exposure, and interrupted -time series analyses were conducted to evaluate the effects of the smoke -free policy and the campaign. RESULTS: For cohorts who entered middle school from 2002 to 2008, the risk of household SHS exposure decreased among both boys and girls. Immediately after implementation of the smoke -free policy, the prevalence of household SHS exposure by period decreased significantly for boys (coefficient, -8.96; p < 0.05) and non -significantly for girls (coefficient, -6.99; p = 0.07). After the campaign, there was a significant decrease in household SHS exposure by cohort among boys, both immediately and post -intervention (coefficient, -4.84; p = 0.03; coefficient, -1.22; p = 0.02, respectively). CONCLUSIONS: A school -admission -cohort effect was found on household SHS exposure among adolescents, which was associated with the smoke -free policy and the campaign. Anti -smoking interventions should be implemented consistently and simultaneously.