The Impact of Tobacco 21 Policy in California and Hawaii on Packs of Cigarettes Sold: A Difference-in-Difference Analysis

Introduction: Tobacco use is the leading cause of preventable disease, disability, and death in the United States. Four out of five U.S. adult cigarette smokers became daily smokers before 21 years of age, and the majority of them began during adolescence. Initiating cigarette smoking during adolescence is more likely to lead to daily smoking, as younger ages of initiation are strongly associated with greater nicotine dependence in adulthood.

Raising the minimum legal age of tobacco sale to 21 years (T21) is an emerging policy option for reducing direct and indirect access to tobacco products by young people, thus contributing to reductions in overall population-level smoking rates. As of September 2018, T21 has been enacted by six states and over 290 localities. Hawaii and California were the first two states to implement T21, both in 2016. This paper contributes to the evidence-base of T21 by examining the impact of T21 in Hawaii and California on packs of cigarettes sold.

Methods We used a difference-in-difference regression method to compare packs of cigarettes sold in intervention states (Hawaii and California) versus control states, pre and post implementation of T21 policy. Utah and Oregon were identified as control states, using a two-stage selection process. These states were identified using a cluster method to select Western states (regionally close to Hawaii and California) with similarities in population composition and tobacco control policy (cigarettes tax rate, tobacco control program funding, smoke-free policies, and smoking prevalence). Because the effective date for T21 was different in Hawaii and California (January 2016 for Hawaii and June 2016 for California), we estimated two alternative models where we excluded the periods when T21 was effective in one state but not the other state. A three-month moving average of packs of cigarettes sold was computed from January 2014 through July 2018. We controlled for secular time trend, seasonal changes, changes in cigarettes tax rates, and total population size.

Results The implementation of T21 in California and Hawaii was associated with an average reduction of 5.91 (CI= -9.27, -2.54) million cigarette packs sold through the period examined. This effect was statistically significant even when controlling for the effects of increases in the cigarette tax rate in California and Oregon.

Conclusion Cigarette sales declined in Hawaii and California after implementation of statewide T21. These findings indicate that raising the minimum legal age for tobacco sales to 21 years may be a viable strategy for states to consider as part of a comprehensive tobacco control strategy.