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).