Seattle’s Minimum Wage Ordinance did not affect supermarket food prices by processing category

Abstract

Objective: To examine the impacts of Seattle’s minimum wage ordinance on food prices by food processing category. Design: Supermarket food prices were collected for 106 items using a UW Center for Public Health Nutrition market basket at affected and unaffected supermarket chain stores at three time points: March 2015 (1-month pre-policy enactment), May 2015 (1-month post-policy enactment), and May 2016 (1-year post-policy enactment). Food items were categorized into four food processing groups, from minimally to ultra-processed. Data were analyzed across time using a multi-level, mixed effects linear regression model at the store and price level stratified by level of food processing. Setting: Six large supermarket chain stores located in Seattle (“intervention”) affected by the policy and six same-chain but unaffected stores in King County (“control”). Subjects: 106 food and beverage items. Results: The largest change in average price by food item was +$0.53 for “processed foods” in King County between 1-month post-policy and 1-year post-policy enactment (P < 0.01). The smallest change was $0.00 for “unprocessed or minimally processed foods” in Seattle between 1-month post-policy and 1-year post-policy enactment (P = 0.94). No significant changes in averaged chain price were observed across food processing level strata in Seattle versus King County stores at 1-month or 1-year post-policy enactment. Conclusions: Supermarket food prices by level of processing do not appear to be differentially impacted by Seattle’s minimum wage ordinance. These results suggest that the early implementation of a city-level minimum wage policy does not alter supermarket food prices by level of food processing.