APPetite: validation of a smartphone app-based tool for the remote measure of free-living subjective appetite

This study determined the validity, reproducibility and usability of a smartphone app - APPetite - for the measure of free-living, subjective appetite. Validity was assessed compared with the criterion tool of pen-and-paper visual analogue scale (VAS) (n 22). Appetite was recorded using APPetite and VAS, one immediately after the other, upon waking and every hour thereafter for 12 h. This was repeated the next day with the order of tool reversed. Agreement between tools was assessed using Bland-Altman analysis. Reproducibility and usability were assessed in a separate experiment (n 22) of two trials (APPetite v. VAS), separated by 7 d. Appetite was recorded in duplicate upon waking and every hour for 12 h using APPetite or VAS. Agreement between duplicate measures was assessed using Bland-Altman analysis and CV was compared between tools. Usability was assessed by comparing compliance and by qualitative evaluation. APPetite demonstrated good criterion validity with trivial bias of 1.65 units/mm.h(-1) between APPetite-and VAS-derived AUC appetite scores. Limits of agreement were within a maximum allowed difference of 10 %. However, proportional bias was observed. APPetite demonstrated high reproducibility, with minimal bias (-0.578 units.h(-1)) and no difference in CV between APPetite and VAS (1.29 +/- 1.42 % v. 1.54 +/- 2.36 %, P = 0.64). Compliance was high with APPetite (92.7 +/- 8.0 %) and VAS (91.6 +/- 20.4 %, P = 0.81). Ninety percent of participants preferred APPetite, citing greater accessibility, simplified process and easier/quicker use. While proportional bias precludes using APPetite and VAS interchangeably, APPetite appears a valid, reproducible and highly usable tool for measuring free-living appetite in young-to-middle-aged adults.