Introduction
EMA
Ecological momentary assessment (EMA) uses digital technologies (eg, smartphones) to gather real-world, real-time data from research participants multiple times per day, thereby overcoming the notable problems with retrospective recall and yielding assessments with excellent temporal resolution and representation of “in the moment” participant experiences [In each of these areas of health behavior research, the use and validity of EMA depend on maintaining EMA compliance across weeks or even months (see Stone and Shiffman [Very little is known about the time course of EMA compliance beyond a few weeks. If compliance declines at a linear rate, the health behavior studies reviewed in the prior paragraph would suggest EMA compliance drops 2%-9% per week. Whereas a 2% per week decline would likely have a modest impact on EMA data [This study seeks to fill this gap in the literature by examining EMA compliance rates over a 9-week period in the context of a randomized controlled clinical trial for smoking cessation among community adults. Based on the work reviewed above, we tested the competing hypotheses that EMA compliance would (1) gradually and linearly decline across weeks or (2) exhibit greater declines in later weeks compared to earlier weeks (ie, accelerating declines tested as a quadratic trend).We also explored candidate predictors of both initial EMA compliance and changes in compliance over time to better understand variables related to assessment completion in clinical EMA samples [We also examined how aspects of the EMA protocol that may have produced a greater burden and less flexibility affected compliance. Specifically, we predicted that initial EMA compliance would be higher, and declines over time would be smaller for (1) participants completing EMA on their own phone compared to a study-provided phone (as the latter often ended up carrying 2 phones, which might have increased burden for completing assessments) [