Understanding Grocery Shopping Behaviour

• Experimental Design and Procedures

The aim of this study is to use a 2 x 2 within-subject crossover design with an online grocery store, to systematically evaluate the effect of the new SSB front-of-pack labels, Nutri-Grade, on diet quality and examine how this effect varies by shoppers' income and education level. To this end, the investigators will be using two different versions of an online experimental grocery store called NUSMart, designed for research purposes. The two versions are described below.

• Overview of Experimental Design

The investigators will recruit Singapore residents aged 21 years or older. Prospective participants will be asked to complete an online screener to determine their eligibility to participate in the study. Those who do not consent or are deemed ineligible will be notified of their ineligibility with an on-screen message.

If interested and eligible, the applicant will then be asked to complete a registration form containing name, mobile number, and email address. Contact information for the Duke-NUS study team will be provided to allow questions to be asked at any point in the consent process and throughout the study. Upon completion of the registration form, NUSMart will create the participant account and a unique ID number (CID) for use throughout the study. Participants will receive an automated email with their unique login details.

Participants will be directed to read the Participant Information Sheet and provide consent. The investigators will provide information on study protocols and participation details without disclosing the intervention arms explicitly, to maintain the integrity of participant responses and hence to ensure validity of results. It will be deleterious to the study to reveal the labels or the differences between study arms before participants complete both shops as this will likely confound participant responses. The consent form will state that in each of the shops there is a 50% chance that the participant will have to make actual purchases i.e. buy the groceries in the cart they checked out. In reality, it will be randomly decided earlier whether shopping trip 1 or 2 is the real shop. This will be achieved via a collaboration with a local online grocery provider, FairPrice.

After obtaining consent, participants will be asked to fill in a baseline survey to collect demographic and health characteristics. The baseline questionnaire includes a question as to whether any household members have a medical condition, such as diabetes or hypertension, which requires limiting the types of foods they eat.

Eligible participants who have completed to this point will enter a participant waiting list, where the study team will manually enroll the participant as active according to the capacity of the study team. Once participants have successfully enrolled in the study they will be informed by email, and are expected to complete two grocery shops (one shop per week) on NUSMart. Participants are expected to complete one shop in one sitting. The investigators will apply a within person design and randomize the order of the two shops. Participants will receive email and text reminders each week to complete their order.

Each participant will be told that they must buy at least one beverage product and that they will make the payment using their credit card & receive their grocery orders. This real-shopping experiment ensures the credibility of the results. Each participant will therefore shop a total of 2 times during the study. This will include 1 shop within each shopping condition (Arm 1 and Arm 2).

During the study, participants will be asked to purchase their weekly groceries the amount of which is similar to their typical grocery shopping for their households, with a specified minimum spend at each shop. A wheel of purchase will be used to determine which one of the 2 shops will the participant actually pay for and receive ordered goods for. Upon completion of their second shop, participants will be asked to fill in a short post-study survey asking for their feedback on the interventions. Participants who successfully complete both shops and all other surveys will be considered as having completed the study. Participants will be provided with the debriefing sheet via email after study completion. For the participants who wish to withdraw midway into the study, the debriefing sheet will be sent to them as soon as possible after they withdraw.

Inclusion criteria

• Singapore resident
• Age 21 and above
• Must be the primary weekly grocery shopper in their household
• Must have an account with our appointed online grocery service provider or is willing to create one.

Exclusion criteria

• Non-Singapore resident
• Non-primary grocery shopper in their household
• Less than 21 years old
• Doesn't have an account with our appointed online grocery service provider and is unwilling to create one.