Table 2. Changes in Taxed and Untaxed Beverage Prices in Cook County, Illinois, Relative to St Louis County and City, Missouria.
| Beverage type | Coefficient estimates (95% CI) | ||||
|---|---|---|---|---|---|
| Posttax period | Postrepeal period | Overall change | |||
| Change in level | Change in slope | Change in level | Change in slope | ||
| Taxed | 1.131 (1.010 to 1.253) | 0.002 (−0.011 to 0.015) | −1.185 (−1.328 to −1.042) | −0.001 (−0.015 to 0.013) | 0.013 (−0.106 to 0.131) |
| SSB | 1.110 (0.999 to 1.222) | 0.004 (−0.008 to 0.016) | −1.190 (−1.321 to −1.059) | −0.003 (−0.016 to 0.010) | 0.008 (−0.102 to 0.118) |
| ASB | 1.206 (1.045 to 1.366) | −0.004 (−0.021 to 0.013) | −1.167 (−1.357 to −0.976) | 0.006 (−0.012 to 0.024) | 0.029 (−0.124 to 0.181) |
| Untaxed | 0.060 (0.007 to 0.114) | −0.000 (−0.006 to 0.006) | −0.014 (−0.074 to 0.045) | 0.000 (−0.007 to 0.007) | 0.045 (−0.028 to 0.118) |
Abbreviations: ASB, artificially sweetened beverage; SSB, sugar-sweetened beverage.
Estimates are from interrupted time series models for the change in intercept and slope in mean price in Cook County relative to St Louis after the Cook County sweetened beverage tax was imposed and after it was repealed, controlling for month. Posttax changes are relative to the end of the pretax period, and postrepeal changes are relative to the end of the posttax period. The overall change in Cook County compared with St Louis at the end of the postrepeal period relative to the end of the pretax period was computed as the sum of the 2 change-in-intercept terms and the 2 change-in-slope terms multiplied by the number of weeks to which they applied. Models were fit by feasible generalized least squares, allowing for first-order autoregressive autocorrelation within each site with site-specific coefficients, and a heteroskedastic error structure assuming no correlation between sites. The price measure used for this analysis is the mean price in cents per fluid ounce across universal product codes (UPCs) in each site and week, weighted by volume sold by UPC from June 2016 to May 2017 in Cook County, St Louis, and the 2-mile border areas surrounding both sites. The analysis included 122 pretax weeks (from March 29, 2015, to July 29, 2017), 16 tax weeks (from August 6, 2017, to November 25, 2017), and 35 postrepeal weeks (from December 3, 2017, to August 4, 2018).