One-year changes in sugar-sweetened beverage consumers' purchases following implementation of a beverage tax: a longitudinal quasi-experiment

Background: Few longitudinal studies examine the response to beverage taxes, especially among regular sugar-sweetened beverage (SSB) consumers. Objective: This study aimed to examine changes in objectively measured beverage purchases associated with the Philadelphia beverage tax on sugar-sweetened and artificially sweetened beverages. Methods: A longitudinal quasi-experiment was conducted with adult sugar-sweetened beverage (SSB) consumers in Philadelphia (n = 306) and Baltimore (n = 297; a nontaxed comparison city). From 2016 to 2017 participants submitted all food and beverage receipts during a 2-wk period at: baseline (pretax) and 3, 6, and 12 mo posttax (91.0% retention; data analyzed in 2019). Linear mixed effects models were used to assess the difference-indifferences in total purchased ounces (fl oz) of taxed beverages in a 2-wk period in Philadelphia compared with Baltimore. Secondary analyses: 1) excluded weeks that contained major holidays at baseline and 12 mo (42% of measured weeks at baseline and 12 mo) because policy implementation timing necessitated data collection during holidays when SSB demand may be more inelastic, and 2) aggregated posttax time points to address serial correlation and low power. Results: There were no statistically significant changes in purchased ounces of taxed beverages in Philadelphia compared with Baltimore in the primary analysis. After excluding holiday purchasing, the tax was associated with statistically significant reductions of taxed beverage purchases at 3 and 6 mo (-157.1 ounces, 95% CI: -310.1, -4.1 and -175.1 ounces, 95% CI: -328.0, -22.3, respectively) but not 12 mo. Analyses aggregating all 6 wk of posttax time points showed statistically significant reductions (-203.7 ounces, 95% CI: -399.6, -7.8). Conclusions: A sweetened beverage tax was not associated with reduced taxed beverage purchases among SSB consumers 12 mo posttax in the full sample. Both secondary analyses excluding holiday purchasing or aggregating posttax time periods found reductions in taxed beverage purchases ranging from -4.9 to -12.5 ounces per day. Larger longitudinal studies are needed to further understand tax effects.