Uncovering Social States in Healthy and Clinical Populations Using Digital Phenotyping and Hidden Markov Models: Observational Study - Imogen E Leaning; Andrea Costanzo; Raj Jagesar; Lianne M Reus; Pieter Jelle Visser; Martien J H Kas; Christian F Beckmann; Henricus G Ruhé; Andre F Marquand (Journal of Medical Internet Research)