Abstract
BACKGROUND: Sugar-sweetened beverage (SSB) taxes have been implemented in various regions as a public health strategy to reduce obesity and associated chronic diseases. While previous research has examined the effectiveness of these taxes, findings remain mixed regarding their impact on long-term health outcomes. This study assesses the effect of Washington State's 2009 soft drink syrup tax on obesity prevalence and related health conditions. This study mitigates selection bias and cross-border purchasing effects, providing a clear picture of the policy's effectiveness. METHODS: We employ the Synthetic Control Method (SCM) to estimate the causal impact of the syrup tax on obesity rates and obesity-related diseases using 1996-2021 data from the Behavioral Risk Factor Surveillance System (BRFSS) and the American Community Survey (ACS). The SCM constructs a counterfactual state to compare against Washington's post-tax obesity trends. Key outcome variables include obesity rates (Body Mass Index [BMI] ≥ 30 and BMI ≥ 35), prevalence of diabetes, hypertension, and high cholesterol. Statistical significance is determined using Monte Carlo simulations ( n = 999 ) with false discovery rate corrections ( p < 0.05 ). RESULTS: Our findings indicate that Washington's syrup tax led to a significant reduction in obesity rates, decreasing by 2.2 to 4.0 percentage points relative to the synthetic control. The tax's effect was most pronounced among college graduates, males, individuals under 65, and White/Asian populations. However, the tax did not yield significant changes in diabetes, hypertension, or high cholesterol prevalence, suggesting a more limited impact on broader obesity-related health conditions. CONCLUSIONS: The study provides evidence that an SSB tax can effectively reduce obesity rates, particularly among certain demographic groups. However, the lack of significant effects on other obesity-related diseases suggests that additional policy measures may be necessary to achieve broader public health improvements. These findings contribute to ongoing policy discussions on the role of taxation in the fight against obesity and highlight the need for targeted interventions to improve the health benefits of such policies.