Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Lee, Eric

Second Advisor

Cashel, Mary Louis


Perfectionism is a transdiagnostic process implicated in several disorders, and is defined in the literature as having standards of performance that are excessively high and often unrealistic, rigidly pursuing these standards, and subsequently measuring one’s own self-worth on their ability to meet these self-set standards (Egan et al., 2011). Perfectionism is related to many negative outcomes for physical and mental health, warranting the need to identify effective treatments that are accessible to individuals experiencing clinical perfectionism. There is a growing need for discrete, single session therapeutic interventions, and research has found that patients who were provided with a brief intervention exhibited accelerated rates of change, compared to patients whose treatment was longer (Baldwin et al., 2009; Kroska, 2018). Therefore, the purpose of this study was to examine the effects of a 90-minute, single-session ACT intervention targeting psychological flexibility for perfectionistic beliefs and behaviors on perfectionism, psychological distress, and well-being utilizing a multiple baseline across participants experimental design. Four individuals completed the following self-report measures at each time point: the Personalized Psychological Flexibility Inventory (PPFI), the Multidimensional Psychological Flexibility Inventory (MPFI), the Frost Multi-Dimensional Perfectionism Scale (FMPS), the Self-Compassion Scale (SCS), the Depression, Anxiety, and Stress Scale-21 item (DASS-21), and the Flourishing Scale (FS). These measures were completed once per week for the five-week baseline period. After baseline, participant engaged in a 90-minute single-session ACT intervention targeting the development of psychological flexibility. For follow-up, participants completed the same measures twice a week for four weeks. Researchers hypothesized that the intervention would increase psychological flexibility, flourishing, self-compassion, and progress towards an idiographic goal, and decrease perfectionism, psychological inflexibility, and psychological distress post-intervention compared to the baseline assessment. A TAR trend analysis was conducted, and Bayes Factors were computed for each individual for each outcome variable to examine within-participant results. A between-case standardized mean difference effect size for SCED was calculated for each outcome variable to examine the results across participants, resulting in a d-statistic. Within participants, while two individuals completed the study with perfectionistic concerns scores below cut offs, this outcome did not change significantly from baseline, with greater evidence for a null effect on this outcome variable for most participants. However, there was evidence for treatment effects for decreasing perfectionistic strivings, psychological distress, and psychological inflexibility and increasing psychological flexibility and flourishing. Across participants, the intervention demonstrated small to large effect sizes. There were small effects on perfectionistic concerns, perfectionistic strivings, psychological distress, and psychological flexibility towards an individual goal. There were medium effects for psychological flexibility and flourishing. Large effects were demonstrated for psychological inflexibility and self-compassion. Overall, the results demonstrate promising evidence for increasing well-being within the context of clinical perfectionism using a single session intervention.




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