Development of the Emoji Faces Pain Scale and Its Validation on Mobile Devices in Adult Surgery Patients: Longitudinal Observational Study

Measuring pain on digital devices using classic unidimensional pain scales such as the visual analog scale (VAS), numerical rating scale (NRS), and faces pain scale (FPS) has been proven to be reliable and valid. Emoji are pictographs designed in colorful form following the Unicode standard. It could be more beneficial to use emoji as faces of FPS on digital devices because emoji can easily fit on most devices and emoji are open-source so no approval would be needed before use. With a concise and user-friendly design, the emoji faces pain scale (Emoji-FPS) might be more generalizable to a wider population and more preferred by digital device users. This study was designed to develop an Emoji-FPS as well as to evaluate its reliability, validity, and preference on mobile devices in adult patients who underwent surgery. A modified Delphi technique with 2 rounds of web-based surveys was applied to obtain panelists' consensus on the sequence of emoji that can best represent 6 levels of pain. The initial candidate sequences of emoji for the Delphi process were constructed referring to 2 well-validated FPSs (Wong-Baker FACES pain rating scale [Wong-Baker FACES] and faces pain scale-revised [FPS-R]). Then, a prospective cohort of patients scheduled to receive perianal surgery was recruited and asked to complete a web-based questionnaire on a mobile device at 5 time points (before surgery [T1], wake up after surgery [T2], 4 hours after surgery [T3], the second day after surgery [T4], and 15 minutes after T4 [T5]). The 4 well-validated pain scales (NRS, VAS, Wong-Baker FACES, and FPS-R) were used as reference scales. After 2 rounds of surveys on 40 Delphi panelists, an Emoji-FPS was finally determined to represent 6 pain levels (0, 2, 4, 6, 8, and 10) from "no hurt" to "hurts worst." For validation, 300 patients were recruited and 299 were analyzed, the mean age of whom was 38.5 (SD 10.5) years, and 106 (35.5%) were women. For concurrent validity, the Emoji-FPS was highly correlated with 4 reference scales with Spearman correlation coefficient ρ ranging from 0.91 to 0.95. Excellent agreements were observed between 4 versions of Emoji-FPS (iOS, Android, Microsoft, and OpenMoji), with weighted κ coefficients ranging from 0.96 to 0.97. For discriminant validity, patients' mean preoperative Emoji-FPS score (T1) was significantly higher than their postoperative Emoji-FPS score (T4) with a difference of 1.4 (95% CI 1.3-1.6; P