Nir Eyal Thank you! I looked through the studies I could find and their citations, but most of them focused on digital vs. paper, which largely concluded that while digital was more available, paper was often a preferred option. In terms of adoption, the best I could get was an approximation from someone who’d done their own research, see the question comment/details section on this Quora answer.
Our ﬁndings are similar: despite most of our users using electronic calendars, every one of them reported using paper calendars even if not regularly; 12 out of 16 interview participants reported using them regularly.
This study from 2011 gives paper calendars a slight edge over digital ones, but it might be outdated.