Table 4.
Overall and food processing group-stratified generalized least-squares regression results for the mean change in item-level price across Seattle (‘intervention’) and King County (‘control’) stores and time, from March 2015 to May 2016, following Seattle’s minimum wage ordinance
| Mean difference in price estimates | Overall | Food processing group | |||
|---|---|---|---|---|---|
|
| |||||
| Group 1: unprocessed or minimally processed foods | Group 2: processed culinary ingredients | Group 3: processed foods | Group 4: ultra-processed foods | ||
| Seattle (relative to King County) | |||||
| Mean ($US) | 0·03 | 0·03 | −0·04 | 0·12 | −0·02 |
| SE ($US) | 0·35 | 0·29 | 0·57 | 0·34 | 0·48 |
| Follow-up 1 (relative to baseline period) | |||||
| Mean ($US) | −0·01 | 0·06 | −0·11 | −0·12 | −0·08* |
| SE ($US) | 0·02 | 0·05 | 0·12 | 0·09 | 0·04 |
| Follow-up 2 (relative to baseline period) | |||||
| Mean ($US) | 0·00 | −0·05 | 0·43*** | −0·08 | 0·03 |
| SE ($US) | 0·06 | 0·04 | 0·12 | 0·18 | 0·12 |
| Seattle × Follow-up 1 | |||||
| Mean ($US) | −0·01 | −0·06 | 0·20 | −0·01 | 0·07 |
| SE ($US) | 0·05 | 0·07 | 0·16 | 0·12 | 0·08 |
| Seattle × Follow-up 2 | |||||
| Mean ($US) | −0·02 | 0·00 | −0·04 | −0·18 | 0·00 |
| SE ($US) | 0·08 | 0·06 | 0·20 | 0·25 | 0·16 |
| Observations (n) | 3776 | 2128 | 245 | 432 | 971 |
| Stores (n) | 12 | 12 | 12 | 12 | 12 |
| R2 within | 0·0000123 | 0·00017 | 0·01110 | 0·00247 | 0·00050 |
| R2 between | 0·000185 | 0·00006 | 0·03340 | 0·00452 | 0·00028 |
| R2 overall | 0·0000221 | 0·00015 | 0·00888 | 0·00262 | 0·00042 |
Baseline, March 2015 (1-month pre-policy enactment); follow-up 1, May 2015 (1-month post-policy enactment); follow-up 2, May 2016 (1-year post-policy enactment).
P values come from Wald tests.
*
P < 0·05,
***
P < 0·001.