Effect of Personalized Incentives on Dietary Quality of Groceries Purchased: A Randomized Crossover Trial

Abstract

Importance: Many factors are associated with food choice. Personalized interventions could help improve dietary intake by using individual purchasing preferences to promote healthier grocery purchases.

Objective: To test whether a healthy food incentive intervention using an algorithm incorporating customer preferences, purchase history, and baseline diet quality improves grocery purchase dietary quality and spending on healthy foods.

Design, setting, and participants: This was a 9-month randomized clinical crossover trial (AB-BA) with a 2- to 4-week washout period between 3-month intervention periods. Participants included 224 loyalty program members at an independent Rhode Island supermarket who completed baseline questionnaires and were randomized from July to September 2018 to group 1 (AB) or group 2 (BA). Data analysis was performed from September 2019 to May 2020.

Intervention: Participants received personalized weekly coupons with nutrition education during the intervention period (A) and occasional generic coupons with nutrition education during the control period (B). An automated study algorithm used customer data to allocate personalized healthy food incentives to participant loyalty cards. All participants received a 5% grocery discount.

Main outcomes and measures: Grocery Purchase Quality Index-2016 (GPQI-16) scores (range, 0-75, with higher scores denoting healthier purchases) and percentage spending on targeted foods were calculated from cumulative purchasing data. Participants in the top and bottom 1% of spending were excluded. Paired t tests examined between-group differences.

Results: The analytical sample included 209 participants (104 in group 1 and 105 in group 2), with a mean (SD) age of 55.4 (14.0) years. They were predominantly non-Hispanic White (193 of 206 participants [94.1%]) and female (187 of 207 participants [90.3%]). Of 161 participants with income data, 81 (50.3%) had annual household incomes greater than or equal to $100 000. Paired t tests showed that the intervention increased GPQI-16 scores (between-group difference, 1.06; 95% CI, 0.27-1.86; P = .01) and percentage spending on targeted foods (between-group difference, 1.38%; 95% CI, 0.08%-2.69%; P = .04). During the initial intervention period, group 1 (AB) and group 2 (BA) had similar mean (SD) GPQI-16 scores (41.2 [6.6] vs 41.0 [7.5]) and mean (SD) percentage spending on targeted healthy foods (32.0% [10.8%] vs 31.0% [10.5%]). During the crossover intervention period, group 2 had a higher mean (SD) GPQI-16 score than group 1 (42.9 [7.7] vs 41.0 [6.8]) and mean (SD) percentage spending on targeted foods (34.0% [12.1%] vs 32.0% [13.1%]).

Conclusions and relevance: This pilot trial demonstrated preliminary evidence for the effectiveness of a novel personalized healthy food incentive algorithm to improve grocery purchase dietary quality.

Trial registration: ClinicalTrials.gov Identifier: NCT03748056.

Figure 1.. Participant Enrollment Flowchart for the Randomized Clinical Crossover Smart Cart Study

Group 1 received the treatment in period 1 followed by an active control in period 2 (AB design). Group 2 received the active control in period 1 followed by the intervention in period 2 (BA design).

Figure 2.. Grocery Purchase Quality Index (GPQI)–16 Scores and Percentage Spending on Targeted Food Groups Among 209 Smart Cart Study Participants

Data points are means, with SEs denoted with error bars. Group 1 (104 participants) was randomized to receive personalized coupons in the initial intervention period followed by an active control in the crossover intervention period. Group 2 (105 participants) was randomized to receive the active control in the initial intervention period followed by personalized coupons in the crossover intervention period.

Figure 3.. Monthly Grocery Purchase Quality Index (GPQI)–16 Scores and Percentage Spending on Targeted Food Groups

Data points are means, with SEs denoted with error bars. Group 1 (104 participants) was randomized to receive personalized coupons in the initial intervention period followed by an active control in the crossover period. Group 2 (105 participants) was randomized to receive the active control in the initial intervention period followed by personalized coupons in the crossover period. The x-axis (months) shows the study duration from September 2018 through May 2019; the end of the initial intervention period occurred in December 2018, and the beginning of the crossover intervention period occurred in February 2019.