Estimated percentage change in calories (kcal) purchased due to incentives across the household income distribution
| Low income | Middle income | High income | χ2-test of equality | |
| Product category: biscuits | ||||
| 10% Price reduction | 4.2*** (4.0 to 4.3) | 4.4*** (4.2 to 4.5) | 4.5*** (4.3 to 4.8) | 6.623** |
| Any price promo. | 35.4*** (33.4 to 37.4) | 39.1*** (37.2 to 41.0) | 36.1*** (33.4 to 38.8) | 7.678** |
| Any volume promo. | 70.7*** (67.8 to 73.5) | 73.7*** (71.2 to 76.1) | 75.2*** (72.1 to 78.4) | 4.749* |
| Observations | 78 009 | 79 432 | 42 441 | |
| Households | 1226 | 1351 | 754 | |
| Product category: crisps | ||||
| 10% Price reduction | 8.7*** (8.3 to 9.2) | 8.7*** (8.3 to 9.2) | 8.9*** (8.4 to 9.5) | 0.400 |
| Any price promo. | 8.3*** (6.0 to 10.6) | 6.9*** (4.7 to 9.0) | 7.8*** (5.2 to 10.4) | 0.829 |
| Any volume promo. | 50.4*** (46.7 to 54.2) | 52.9*** (49.9 to 55.9) | 53.8*** (49.9 to 57.8) | 1.656 |
| Observations | 48 281 | 55 091 | 32 014 | |
| Households | 1211 | 1338 | 751 | |
| Product category: savoury snacks | ||||
| 10% Price reduction | 6.2*** (5.9 to 6.6) | 6.5*** (6.2 to 6.9) | 6.4*** (6.0 to 6.7) | 1.889 |
| Any price promo. | 25.2*** (22.8 to 27.6) | 27.3*** (24.9 to 29.7) | 26.6*** (23.8 to 29.5) | 1.474 |
| Any volume promo. | 76.2*** (72.9 to 79.5) | 77.5*** (74.2 to 80.8) | 79.8*** (76.0 to 83.6) | 1.941 |
| Observations | 40 190 | 47 868 | 30 578 | |
| Households | 1212 | 1342 | 745 |
95% CI in brackets *p < 0.10, **p < 0.05, ***p < 0.01.
Number of observations within categories varies based on the number of purchases per household.
All models include age of main shopper, age2 of main shopper, household size, time in panel (years), time since last purchase (weeks), and year dummies (full results available in online supplemental appendix).