摘要：Objectives. We aimed to investigate population-level changes in smoking initiation during California's Tobacco Control (CTC) Program from 1990 to 2005, a period during which tobacco industry marketing practices also changed. Methods. We used a discrete time survival analysis of data from the California Tobacco Survey to model changes in age of first smoking experimentation across birth cohorts. Results. Smoking initiation patterns were stable across cohorts aged 9 years or older at the start of the CTC program. For children entering preadolescence since 1990, initiation declined with each more recent cohort. By 2005, the observed decline in experimentation was 80% for male participants and 92% for female participants at age 12 to 14 years; by age 15 to 17 years, 10% of Californian adolescents had experimented in 2005 compared with 45% in preprogram cohorts. However, rates of new experimentation after age 17 years did not change, except for a recent increase in late experimentation (after age 20 years) among young adult men. Conclusion. Our models suggest that the CTC program greatly reduced adolescent smoking initiation among younger adolescents. Late experimentation may have recently increased among young adult men in California, coincident with an increase in tobacco industry marketing aimed at young adults. Since the 1960s, adolescent smoking rates have changed in response to the competing influences of tobacco industry marketing campaigns 1 – 3 and public health tobacco control programs. 4 , 5 Reducing adolescent smoking has been a primary goal of the California Tobacco Control (CTC) Program, 6 the longest-running large tobacco control program in the world. As an evaluation component, this program sponsors a population survey of tobacco use every 3 years. Previous survey estimates indicated that the CTC Program was associated with a lower age-specific prevalence of smoking from age 12 years, which was probably a consequence of reduced experimentation. 5 However, it is not clear whether these age-specific changes led to an overall reduction in lifetime smoking initiation within a birth cohort, especially given the apparent effectiveness of recent tobacco advertising targeting young adults. We investigated changes in the trajectories of smoking experimentation across the age window of 10 to 24 years, in which almost all first experimentation has been documented to occur. 7 Previously, an age-period-cohort model 8 identified that smoking experimentation for California was stable for cohorts born before 1979. Subsequent cohorts, those aged 12 years or younger when the California program started in 1990, had lower experimentation levels on average over the adolescent years. However, the model in that analysis used additive effects for age, period, and cohort, with the consequence that, for example, changes in experimentation rates at a given time were averaged across cohorts and ages. Period and cohort effects, which can identify time changes, applied equally across all ages. Thus, that analysis was unable to identify changes in smoking uptake at specific ages within the age window of 10 to 24 years. This may be of concern, because other interventions that reduced smoking in early adolescence were shown to not be associated with reduced smoking in later years. 9 , 10 In addition, there is specific concern that tobacco industry marketing campaigns have changed to target young adults, and this may have increased rates of smoking initiation in young adulthood. 11 Recent contributions to the methodologic literature 12 – 17 have addressed shortcomings of age-period-cohort models in identifying age- and period-specific effects. 18 , 19 Incorporating suggestions from this literature, we modeled age-specific changes in the trajectory of smoking initiation among young Californians from 1990 to 2005. We hypothesized that age-specific changes have occurred in the pattern of smoking uptake among recent birth cohorts.
