Beverage consumption and perceived healthfulness among parents, and investigation of spillover effects: Insights from the Seattle Sweetened Beverage Tax

Sugar-sweetened beverage (SSB) taxes are generally adopted with the goal of reducing SSB consumption and improving public health. Extensive research on local SSB excise taxes in the US shows that taxes consistently increase prices and decrease purchasing of taxed beverages in the taxed jurisdiction. Evidence of impacts on SSB consumption, however, is less consistent. In January 2018, Seattle implemented a 1.75-cent-per-ounce tax on the distribution of SSBs. While the tax was associated with fewer SSB purchases in Seattle, SSB consumption unexpectedly decreased in Seattle and the nearby nontaxed comparison area in King County in a cohort study of families with lower income. We hypothesized that the Seattle tax influenced comparison area residents to reduce SSB consumption, known as spillover effects. We also hypothesized that parents responded differently to the SSB tax as compared to other adults as an alternative possible explanation for the cohort findings. Considering the essential role of parents in their child’s dietary patterns and the limited evidence around tax spillover effects, the overall goal of this dissertation was to developing a better understanding of how perceived healthfulness and consumption of SSBs may have changed among families with lower income in Seattle and nearby areas. In Chapter 1, we conducted qualitative interviews with 35 former participants of the cohort study and learned that health was the primary reason that parents in Seattle and the comparison area decreased their SSB consumption one- and two-years post-tax. Parents said the tax had some influence on their SSB consumption as well, including some comparison area parents who were exposed to media coverage of the tax or beverage prices while shopping in Seattle. In Chapter 2, we analyzed a large panel of retail scanner data using linear difference-in-differences regression to investigate whether the tax influenced SSB purchasing in communities near Seattle as a form of spillover tax effects. We did not find evidence of spillover effects of the SSB tax in communities near Seattle relative to a matched comparison area, although we observed a 20% net decline in volume sold in Seattle relative to a matched comparison area. In Chapter 3, we analyzed repeated cross-sectional survey data from a Seattle tax evaluation study to examine whether associations between the SSB tax and perceived healthfulness and consumption of SSBs differed between adults with and without children in the home. Using linear and logistic difference-in-differences regression, we did not observe associations between the SSB tax and these outcomes among adults with or without children. Findings highlight the need to understand potentially unique experiences of tax spillover among households with lower income and strategies that support parents’ motivations to reduce SSB consumption post-tax.