TABLE 2.

Difference-in-differences regression results for changes in beverages purchased, total spending, and tax avoidance following implementation of a beverage tax (n = 603)¹

	Difference-in-differences estimate	Lower CI	Upper CI	P value	Corrected P value
Primary outcome-purchasing
Purchased taxed beverages (ounces)
Tax effect at 3 mo	−29.3	−123.3	64.7	0.542
Tax effect at 6 mo	−47.3	−144.8	50.3	0.343
Tax effect at 12 mo	−10.1	−106.7	86.6	0.839
Purchased taxed beverages excluding holidays (ounces)
Tax effect at 3 mo	−157.1	−310.1	−4.1	0.044
Tax effect at 6 mo	−175.1	−328.0	−22.3	0.025
Tax effect at 12 mo	−166.6	−350.0	16.9	0.075
Secondary purchasing outcomes
Purchased nontaxed beverages (ounces)
Tax effect at 3 mo	62.1	−69.2	193.3	0.355	0.355
Tax effect at 6 mo	−1.3	−124.3	121.6	0.983	0.983
Tax effect at 12 mo	75.0	−55.1	205.0	0.260	0.260
Percent of taxed beverages purchased outside border (%; Philadelphia only, n = 306)2
3 mo after tax	6.6	0.9	12.3	0.025	0.049
6 mo after tax	10.0	4.4	15.6	<0.001	<0.001
12 mo after tax	12.5	6.8	18.2	<0.001	<0.001
Secondary spending/self-reported outcomes
Total food and beverage spending ($)
Tax effect at 3 mo	0.3	−27.6	28.2	0.983	>0.999
Tax effect at 6 mo	−4.0	−32.1	24.1	0.780	>0.999
Tax effect at 12 mo	17.0	−11.5	45.5	0.244	0.488
Percent spent on taxed beverages (%)
Tax effect at 3 mo	−0.9	−3.8	2.0	0.560	>0.999
Tax effect at 6 mo	0.4	−2.5	3.4	0.784	>0.999
Tax effect at 12 mo	−0.5	−3.5	2.4	0.720	0.720
Self-reported frequency of cross-border shopping (Philadelphia only, n = 306)3
6 mo after tax	0.12	−0.18	0.41	0.439	>0.999
12 mo after tax	0.25	−0.05	0.54	0.100	0.300

¹All purchasing and spending patterns estimates refer to a 2-wk period. Purchase, total spending, and taxed ounces purchased outside taxed jurisdiction models adjusted for age, gender, race/ethnicity, education, household size, BMI, and collection week of the month. The difference-in-differences effect of the tax was obtained by including interaction terms for location (Philadelphia compared with comparison) and time period (3, 6, or 12 mo) except for self-reported frequency of purchasing in neighboring counties. Secondary outcomes were adjusted using a Bonferroni–Holm correction for 2 tests for purchasing outcomes and 3 tests for spending and self-report outcomes.

²Model also adjusted for the distance from participants’ home to Philadelphia city border and total ounces of taxed beverages purchased.

³Items on self-reported purchasing outside the taxed jurisdiction were measured on a 5-point scale. This question was excluded at 3 mo due to a survey error. The effect of the tax for this outcome was obtained by time period (6 or 12 mo).