Date of Award:

12-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Psychology

Committee Chair(s)

Michael E. Levin

Committee

Michael E. Levin

Committee

Michael P. Twohig

Committee

Ty B. Aller

Committee

Gretchen G. Peacock

Committee

Sarah Schwartz

Abstract

Digital mental health interventions offer a more accessible, affordable, and flexible option for mental health support. These apps and websites draw from the same therapeutic models as face-to-face therapy, but are available on demand at a fraction of the cost. In exchange, digital formats give up the personal relationship, accountability, and scheduled structure that keep people connected to treatment. This places a greater burden on users to stay involved on their own, and as a result, engagement is widely believed to be the main bottleneck limiting the impact of digital mental health care.

This dissertation examined engagement in digital programs based on acceptance and commitment therapy (ACT). ACT is a therapy that works through improving psychological flexibility, which is one’s ability to pursue values while making room for difficult thoughts and feelings. Combining results from more than 50 clinical trials, we found that these programs produce small but reliable improvements across a range of mental health outcomes. We then tested whether trials with more engaged participants showed stronger effects. Trials in which participants found the program more satisfying and easier to use tended to show larger improvements. Among usage measures, however, only the proportion of participants who started the program mattered. The quality of participants' experience may therefore be more closely tied to a program's effectiveness than to what extent it is used. Our final study looked at coaching as an additional support. Coaching helped participants complete more of the program, which strengthened their psychological flexibility, which in turn reduced distress. Coaching also showed benefits beyond this pathway, directly impacting psychological flexibility and distress.

Taken together, these studies suggest a shift in how engagement is understood. Rather than treating usage as the goal, developers may gain more by attending to the quality of the experience a program provides. Many of the features examined in this dissertation, including program length, reminders, human support, and design quality, are variables under the direct control of researchers and developers. Identifying which of these matter most would give future work a basis for building effective digital interventions that individuals want to use.

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