Published on in Vol 21, No 12 (2019): December
Preprints (earlier versions) of this paper are
available at
https://preprints.jmir.org/preprint/15166, first published
.
1 Chelsea and Westminster Hospital, NHS Foundation Trust, London, United Kingdom
2 Department of Surgery and Cancer, Imperial College London, London, United Kingdom
3 School of Public Health, Imperial College London, London, United Kingdom