4. Discussion
appetite
The study developed and validated a digital tool for appetite measurement in digital clinical trials while leveraging participants’ own devices. The results indicated that digital VAS can be as sensitive as paper VAS for appetite measurements.In the primary analysis, it was found that 4 of the 5 appetite ratings did not differ significantly between the two methods assessed; however, prospective consumption was found to be significantly lower when measured by digital VAS than measured by paper VAS. The significant difference may be due to the increased power resulting from the large sample size in the study and the capacity to render very small differences significant. As envisioned, the difference in the least squares means was only 1.1 out of 100 points. A difference at this magnitude is likely to be non-relevant for practical purposes. Moreover, results from the Bland and Altman analysis, as well as results from the sensitivity analysis, further confirmed that both methods provided similar results.Theoretically, participants may give the same response when they are asked the same question using different tools by recalling their previous response. However, the VAS data was captured on a continuous scale with responses transcribed to a numeric value between 0 and 100 by the researchers, and participants did not directly see the numeric value from the survey they completed. Thus, recalling the exact position they marked on a VAS could be difficult in most cases unless they intentionally measured it. Additionally, to reduce the possibility of participants directly copying the answer from one tool to another tool, the app was programmed such that when the digital VAS was submitted, the data entry could not be retrieved by the participant. Similarly, when the paper VAS was completed, participants were asked to place it into a designated return envelope before completing the digital VAS.Some recent studies have used mobile phones to collect appetite data using a categorical scale. For example, the PREDICT 1 study used the Zoe study app to collect hunger data using a scale from 0 to 10 in free living conditions [One potential technical challenge in developing a digital VAS with participants’ own devices is that the length of the digital scale displayed on the screen may vary depending on the screen size of a smart phone or the orientation of the device (whether the phone is held in portrait or landscape position). This may not be an issue for responses captured by a 11-point Likert scale since these are essentially multiple choice questions displayed on the screen. To address the orientation issue, the app was programmed in such a way that the appetite survey could only be displayed and completed when the phone was detected to be held in landscape mode. We chose landscape mode rather than portrait mode because the physical length of a digital horizontal line in that situation would be closer to 100 mm, which is the standard length on paper VAS. Data from our study indicated that 74 participants used the iPhone (models varied from iPhone 8 to iPhone 13 Pro Max) and 28 used Android devices (manufacturers included LG, Samsung, Google, and OnePlus). The length of digital VAS displayed on smart phone screens in this study varied between 85 and 128 mm with a median of 105 mm, and 80% of the length data were between 90 and 110 mm. Visual examination of the appetite data did not reveal any specific data pattern related to the physical length of the scale, indicating that length may not be a critical factor. Indeed, Chaput et al. [Compared to clinical trials conducted in traditional research facilities, digital studies conducted virtually may have greater external generalizability since participants can be followed up in the real world. However, this brings the potential issue of compliance. As appetite feelings are time dependent, responding to appetite surveys in a timely manner is crucial to ensure the quality of research data. In our primary analysis, we excluded a few subjects who completed multiple appetite surveys around the same time later in the day. We also conducted a sensitivity analysis by excluding subjects who responded to survey tasks at least 10 min late on average. The reason for not excluding these participants in the primary analysis was because missing data can be imputed using the last observation carried forward method in clinical research. When dealing with missing data, appetite data being late by 10 min could be a better option than replacing the missing data with an earlier appetite response, which was usually 30 min earlier in this study. Eleven percent of participants were excluded based on this criterion in the sensitivity analysis. Our compliance was comparable to a previous study reporting that 82% of responses were received within 15 min after a text was sent to participants to report their appetite in a free-living condition [Our study has several clear strengths. It provides a newly validated digital technology that may be used in future studies with the use of mobile devices from participants in a cost and time efficient manner, thus eliminating the requirement of device shipping and return using existing EARS. Our study also included a large sample size with participants recruited remotely in the US, demonstrating that this new tool can be used in large-scale virtual trials without geographic restrictions for participation. Moreover, the digital VAS was validated for use in various smart phone models available on the market today. Nonetheless, our study has certain limitations. First, test-retest reproducibility was not assessed. The reproducibility of paper VAS and EARS have been shown previously [In conclusion, the mobile app-based digital VAS is a validated and preferred tool for measuring appetite in the real world, compared to the traditional paper-based VAS.