Published on in Vol 6 , No 11 (2018) :November
Preprints (earlier versions) of this paper are
available at
https://preprints.jmir.org/preprint/12237, first published
.

1 ITACA, Universitat Politècnica de València, Valencia, ES
2 Department of Computer Science, University of Tromsø, Tromsø, NO
*all authors contributed equally