Document Type


Date of Degree

Summer 2018

Degree Name

PhD (Doctor of Philosophy)

Degree In


First Advisor

O'Hara, Michael W.

First Committee Member

Vander Weg, Mark W.

Second Committee Member

Marchman, James N.

Third Committee Member

Denburg, Natalie L.

Fourth Committee Member

Markon, Kristian E.


A large body of research has examined the appropriate time course of psychotherapy across a variety of therapeutic modalities. Research in the area of Acceptance and Commitment Therapy (ACT) has indicated the efficacy of single-session interventions in improving anxiety, depression, and even weight loss. These findings, though promising, are accompanied by the question of how much ACT is enough to make a statistically and clinically significant difference in symptoms. The present study sought to clarify this question among individuals with depression.

Adults (N = 271) with elevated depressive symptoms were recruited via mass emails for a study comparing the relative effectiveness of time-variant single-session ACT interventions (90 minutes, 3 hours, 6 hours). Inclusion criteria included PHQ-8 score 10, no history of TBI, no current psychotherapy, and no medication changes in the past 60 days. Eligible participants completed a screening interview, which included modules from the M.I.N.I. Exclusion criteria included active suicidality, past or current mania, and past or current psychoses. If interested in participating (n=351), eligible participants could complete the baseline measure after enrolling in the study. Participants were randomized to a single-session 90-minute, 3-hour, or 6-hour group ACT intervention. About half (51.2%) of enrolled and randomized participants completed their assigned group intervention. Follow-up assessments were completed at 1-month and 3-months post-intervention with limited attrition. Longitudinal mixed-effects modeling was used to examine change over time and between conditions.

Findings indicated that depressive symptoms and avoidance decreased over time, and social satisfaction increased over time. Differences between conditions and interactions between time and condition were not observed. Equivalency analyses revealed that the 3- and 6-hour groups were not within the margin of equivalence in terms of depressive symptoms. Mindfulness analyses revealed that at 3-month follow-up, the 3- and 6-hour groups reported higher mindfulness than the 90-minute group.

The findings have public health implications in terms of reaching a larger number of patients with increased efficiency. Given the far greater patient demand than number of therapists available, increased access and efficiency are of great importance. The results also suggest that individuals with depression can make rapid, sustainable changes, and this is of critical importance clinically. Limitations included a homogenous sample of primarily white, highly educated females, and the lack of a no-treatment control group. The findings of the current study indicate that brief group ACT interventions can result in change in both processes (avoidance, mindfulness) and functioning (depressive symptoms, social satisfaction) months after the single-session intervention. Future research should examine the effectiveness of brief interventions with other symptomatology as compared to a no-treatment control or a more traditional course of psychotherapy.


Acceptance and Commitment Therapy, Brief therapy, Depression, Experiential avoidance, Mindfulness


xi, 79 pages


Includes bibliographical references (pages 44-51).


Copyright © 2018 Emily Brenny Kroska

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