What question did this study set out to answer?

This study aims to evaluate the impact of a sugar-sweetened beverage tax on purchasing behaviors in nearby communities, focusing on spillover effects.

February 6, 2026Open Access

Investigation of spillover effects of a sugar-sweetened beverage tax on beverage purchasing in a nearby, non-taxed area: A quasi-experimental, difference-in-differences analysis

Key Points

This study aims to evaluate the impact of a sugar-sweetened beverage tax on purchasing behaviors in nearby communities, focusing on spillover effects.
Utilized retail scanner data from 3,531 beverages across 127 retailers in King County.
Applied Mahalanobis distance for matching comparison areas based on demographic data.
Conducted linear difference-in-differences analysis for sales from two years before and after tax implementation.
Estimated tax effects in Seattle for context regarding potential impacts in surrounding areas.
In King County, no significant change was observed in taxed beverage volume with a mean difference of 172 liters (95% CI: −1,396, 1,740; P = 0.83).
Evidence suggested increased volume sold for some taxed and nontaxed beverages in King County relative to a matched area.
In Seattle, there was a significant decline in taxed beverage volume sold, with a mean difference of −3,628 liters (95% CI: −4,622, −2,634; P < 0.001).
No evidence of spillover effects was found in nearby communities regarding reduced SSB sales.

Abstract

Evidence suggests that sugar-sweetened beverage (SSB) taxes reduce SSB purchasing and improve health outcomes in the taxed area. The extent to which purchasing also changes in nearby communities due to tax signaling effects is unclear. The objective of this study was to assess whether the SSB tax in Seattle, Washington, USA, influenced SSB purchasing in nearby communities within the same media market. We used retail scanner data on weekly sales of 3,531 beverages from 127 retailers in King County excluding Seattle and its bordering area (KC), and 243 retailers in a matched comparison area outside the regional media market. Matching was done via Mahalanobis distance based on pre-tax, county-level demographic measures from the American Community Survey. We estimated linear difference-in-differences in mean volume sold of taxed and nontaxed beverages comparing two years before (2016−2017) and after tax implementation (2018−2019) adjusting for beverage-level fixed effects. We also estimated the difference-in-differences in Seattle versus a matched comparison to estimate the tax effect in Seattle as context for potential effects in KC. For taxed beverages, the mean difference-in-differences in volume sold in KC was 172 liters (95% CI: −1,396, 1,740; P = 0.83), reflecting a 1% change from pre-tax levels in KC for a given beverage. There was suggestive evidence of increased volume sold for taxed and nontaxed soda, and taxed multipack beverages in KC relative to the comparison area. In Seattle, the mean difference-in-differences in volume sold for taxed beverages was −3,628 liters (95% CI: −4,622, −2,634; P < 0.001), reflecting a 20% decline for a given beverage in association with the tax. We did not find evidence of spillover effects in the form of reduced volume sold of SSB in communities near but not bordering the tax in Seattle. Studies in other contexts are needed to investigate spillover on purchasing as well as possible explanations for observed increases in purchases of taxed and nontaxed soda.

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