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Abstract
Minimum wage policies may increase the capacity of low wage workers to achieve higher quality diets through greater food purchasing power. However, limited evidence is available on the effect of minimum wage policies on consumer food prices and even fewer studies perform cost analyses that include measures of food quality. One hypothesis is that the Seattle Minimum Wage Ordinance (SMWO) may result in changes in food prices differentially by food quality such that higher quality foods (i.e., more nutrient dense foods) have a higher increase in prices than lower quality foods. The present study tested: a) whether there is a change in food prices in response to the SMWO 2-years post-implementation, and b) whether there is a differential change in food prices by food quality such that nutrient dense foods had a higher increase than nutrient poor foods. Market basket data on 106 food and beverage items were collected at six supermarket chain stores affected by the SMWO (i.e., treatment) and at six same-chain supermarkets unaffected by the ordinance (i.e., control) at four time points between March 2015 and May 2017 (i.e., 1-month pre-policy implementation and at 1-month post, 1-year post, and 2-years post-policy implementation). The present study applied a nutrient density metric to the SMWO market basket to test these hypotheses. Item-level nutrient density scores were calculated and categorized by quartile using the Nutrient Rich Foods 9.3 index. A series of statistical analyses were conducted to examine price differences attributable to SMWO overall and of foods by nutrient density quartile: a) between treatment and control supermarket chains, b) across treatment and control supermarkets over time, and c) price differences attributable to SMWO. First, there were no overall market basket price changes over time or attributable to SMWO. Second, food prices by nutrient density quartile did not differ significantly between treatment and control supermarkets at any time point. Third, there were no significant price changes for any nutrient density quartile at affected or unaffected locations over time (baseline and 3 follow up time points). Fourth, there were no significant average item price changes over time for any of the nutrient density quartiles attributable to SMWO. In conclusion, no evidence was found of a pass-through effect on supermarket food prices in response to an increased city-wide minimum wage overall or differentially by food quality.
