Evaluating the impact of the California 1995 smoke-free workplace law on population smoking prevalence using a synthetic control method.

The objective of this study is to assess the impact of the California 1995 Smoke-Free Workplace Act (SFWA) on cigarette smoking prevalence in the population. We used survey responses related to cigarette smoking from the Behavioral Risk Factor Surveillance System (BRFSS) from 1990 to 2000. We utilize a synthetic control method which creates a weighted combination of control states to produce a single 'synthetic' control group to best approximate the counterfactual trend in California in the absence of the SFWA. Variables known to be associated with smoking were included to weight each state in the pre-intervention period as medians by state and included: distribution of race/ethnicity (White, Black, Asian, Hispanic), sex (Male/Female), marital status (married/unmarried), high school education (yes/no) and employment status (yes/no). We find evidence that there was a small decrease in population smoking prevalence in California in the year immediately following the SFWA, but this effect was not sustained beyond 1995. We hypothesize that one potential explanation for the lack of prolonged impact on population smoking prevalence is that there are sustained effects from the passage of 1989 California Proposition 99, which enacted an excise tax on tobacco products. Understanding how workplace smoking ban legislation affects population smoking behaviors is necessary to better inform policy development in other states and counties and to improve existing policies. Future work should consider the impact of smoking legislation impacts subgroups of the population by socioeconomic status, occupation or race/ethnicity.