How have smoking risk factors changed with recent declines in California adolescent smoking?

To compare predictors of smoking initiation in two longitudinal studies in California conducted during periods when adolescent smoking prevalence was increasing (1993-96) and decreasing (1996-99).

Cohorts of 12-15-year-old never smokers were identified from the cross-sectional 1993 and 1996 California Tobacco Surveys (large population-based telephone surveys) and followed-up 3 years later (1993-96, n = 1764; 1996-99, n = 2119).

We compared cohort transition rates to any smoking by follow-up in risk groups defined by known predictors of smoking initiation at baseline. Besides examining predictors individually, risk groups were defined using a multivariate analysis.

Overall, transition to any smoking by follow-up occurred in 38.3 +/- 4.0% (% +/- 95% confidence interval) of never smokers in the 1993-96 cohort and 31.1 +/- 2.6% in the 1996-99 cohort. For most predictors, the transition rate for adolescents with the characteristic was the same or only slightly lower in the 1996-99 cohort compared to the 1993-96 cohort, but the transition rate in those without the characteristic was generally much lower, thus increasing the power of the predictor. The multivariate analysis confirmed that compared to the 1993-96 cohort, transition occurred much less often in the 1996-99 cohort for adolescents at low rather than at medium or high risk of future smoking.

The turnaround in California adolescent smoking in the mid-1990s, when smoking began to decline, appears to come primarily from adolescents already at low risk of future smoking (as defined by a variety of predictors), who transitioned to smoking at much lower rates than previously.