2.3. Participants and Procedures
obesity, WL, diabetes
OBESITY, HYPERTENSION, SHOP, DIABETES
Participants were recruited from July to August 2021 from the Kantar online web panel of Saudi Arabian citizens and residents. Prospective participants were asked to complete an online screener to determine their eligibility. They were eligible if they were aged 18 years or older, were KSA residents, able to read and write in Arabic, and were the primary grocery shopper for their household. Those interested and eligible were asked to complete an online consent form. Participants were made aware that there were multiple versions of the online grocery store but were not told of the nature of the study; those who consented were exposed only to the version of the store into which they were randomized.Once they consented, participants were directed to a baseline survey collecting their demographic characteristics, including age, sex, education level, housing type, monthly household income, and the underlying diet-related health conditions of their household members (e.g., overweight, obesity, diabetes, and hypertension). Upon completion of the baseline survey, participants were randomly assigned to one of the three study arms with equal probability and landed in a randomly chosen food subcategory to start shopping. Participants were then asked to complete a single hypothetical shopping trip as though all meals and snacks for their household members for the next 7 days would be made from foods and beverages purchased from this shopping trip. In efforts to encourage shoppers to take the task seriously, they were also required to spend a minimum of 150 Saudi riyals (SAR, equivalent to 40 US dollars) per household member and to shop in at least four food categories. This minimum amount was determined based on the average per capita monthly spending on foods and beverages (excluding consumption away from home) reported in the 2018 KSA Household Expenditure Survey, with inflation and taxes accounted for. Those who were assigned to the NS arm were shown a brief introductory video about the modified NS label. They were able to watch this video again at any time during their shopping trip. We did not show a similar video to participants assigned to the WL arm because we believed that messages on WL (‘high in [nutritional component X]’) are relatively straightforward. Panelists who completed the study received compensation in points according to Kantar’s in-house incentive protocols.The use of a web panel enabled us to collect data relatively quickly, at low cost, and from a geographically diverse population of shoppers in KSA. Once participants completed their shopping and clicked on “check-out,” they were asked to take a brief post-study survey that included questions that tested how well they understood the labels and video (if applicable), as well as an open-ended feedback question.A power calculation revealed that 602 participants were required to detect a standardized effect size of 0.3 in outcomes between arms, assuming a two-tailed 