Each participant was interviewed twice, 1 week apart, before and after they had used their allocated app. Interviews included mostly qualitative, but also a small number of quantitative (ie, 1-10 rating scales) elements. The first interview provided a short, baseline assessment of the individual’s smoking habits and history, as well as of their perceptions of digital therapeutics and mobile apps in health care. Participants were also given standardized instructions regarding app use. Interviewers were instructed to neither encourage nor discourage the participants’ smoking behavior, to minimize bias.