The impact of Seattle's Sweetened Beverage Tax on beverage prices and volume sold.

On January 1, 2018 the city of Seattle, WA, implemented a 1.75-cent per ounce (oz) Sweetened Beverage Tax (SBT) on sugar-sweetened beverages with at least 40 calories per 12 oz. This study drew on universal product code-level store scanner data and used a pre-post intervention-comparison site difference-in-differences (DID) study design to assess the impact of the SBT on taxed beverage prices in Seattle, the volume sold of taxed beverages in Seattle and in its 2-mile border area (cross-border shopping), and the volume sold of untaxed beverages (substitution) relative to changes in its comparison site of Portland, OR. The DID results showed that, on average, in the first year post-tax implementation, prices of taxed beverages rose by 1.03 cents per oz (p < 0.001) corresponding to a 59% tax pass-through rate. Volume sold of taxed beverages fell, on average, by 22% (p < 0.001) in the first year following the implementation of the tax. Volume sold of taxed beverages fell to a greater extent for family- versus individual-size beverages (31% versus 10%) and fell to a greater extent for soda (29%) compared to all other beverage types. Moderate substitution to untaxed beverages was found - volume sold of untaxed beverages increased by 4% (p < 0.05). The results revealed no significant increases in the overall volume sold of taxed beverages in the 2-mile border area of Seattle relative to its comparison site suggesting that tax avoidance in the form of cross-border shopping did not dampen the impact of the tax.