2.5. Research Procedure
appetite
Eligible participants were followed up with instructions to install the OTS app and answer questions related to their smart phones, such as manufacturer and model information, and they were asked to provide a shipping address. Study packages were shipped to participants, with test foods and materials including BelVita biscuits, a measuring cup, a ruler, paper appetite surveys, and return envelopes. Upon receiving the package, participants were asked to take a picture of the items received and upload the picture using the OTS app to confirm the items were received without damage. Participants were also asked to complete a paper appetite survey followed by uploading a picture of the completed paper survey, as well as a digital appetite survey, both using the OTS app, as a practice prior to the study. When completing the digital appetite survey, participants were also asked to use a ruler to measure the length of the digital VAS displayed on the screen of their smart phone and report the data to the study team via the OTS app.On the day prior to the first test session, participants were reminded to avoid heavy physical activity and alcoholic drinks and to maintain their normal diet. Later that day, participants were reminded not to consume any food or beverage, except water, after 10:00 p.m. On the next day, participants were instructed to prepare the test food for breakfast at 7:50 a.m., which included 1 or 2 servings of the biscuits with 8 ounces of water using a measuring cup, take a picture of the breakfast, and upload it using the OTS app. At 8:00 a.m., participants were instructed to complete both a digital and paper appetite survey, in random order, and start eating breakfast. They were asked to finish the entire breakfast in 15 min. Immediately after breakfast, participants were asked to complete another set of digital and paper appetite surveys. Subsequently, participants were asked to not eat or drink anything in the next four hours and avoid moderate or heavy physical activity, while not reading books, watching TV, or browsing the internet for any content related to food. Another set of digital and paper appetite surveys was completed 30, 60, 90, 120, 180, and 240 min after breakfast. Each time, the order of the digital versus paper appetite survey was randomized by asking participants to randomly choose from the two options in the app. After completing a paper survey, participants were asked to upload a picture of the completed survey using the OTS app and then immediately place the completed survey in the designated return envelope.The procedure for the second test session was similar to that of the first test session, except that a different serving of biscuit was consumed and a final survey about the participants’ experience was administered. The survey collected information on preference for paper versus digital VAS and ease of use for each method using a 5-point scale. After the final survey, participants were debriefed and informed that the primary goal of the study was to compare the digital vs. paper VAS for appetite measurements. Participants were asked to return the completed paper appetite surveys to the study team by mail.