(PS8-C52) Measuring Psychological (In)flexibility: A Psychometric Evaluation and Comparison of Existing Measures

Psychological (in)flexibility, the tendency for behavior to be guided by psychological reactions rather than personal values, is a central tenet of acceptance and commitment therapy (ACT; Hayes, Strosahl, & Wilson, 2012). Although several self-report measures of this construct have been developed, research has identified potentially serious problems in some of the most widely used measures. Additionally, there is a lack of consensus regarding which of these measures is most theoretically and psychometrically sound, and the most recently developed measures have not been independently evaluated. In the present study, contrast analysis was used in to evaluate the construct validity of five self-report measures of psychological (in)flexibility by directly comparing the relative position of each measure within a network of criterion variables (Westen and Rosenthal, 2003).

Adult participants (N = 474), recruited via Amazon Mechanical Turk, completed a battery of self-report measures via a secure online portal. Measures of psychological (in)flexibility included the Acceptance and Action Questionnaire-II (AAQ-II; Bond et al., 2011), Acceptance and Action Questionnaire-3 (AAQ-3; Ong et al., 2019), Multidimensional Psychological Flexibility Inventory (MPFI; Rolffs et al., 2018), Comprehensive Assessment of Acceptance and Commitment Therapy Processes (CompACT; Francis et al., 2016), and the Personalized Psychological Flexibility Inventory (PPFI; Kashdan et al., 2020). The sample was primarily male (55.3%), White (84.4%), and the average age was 36.6 (SD = 9.6). Participants who completed this study were financially compensated for their time.

The AAQ-II, AAQ-3, and MPFI Inflexibility scale demonstrated consistently high reliability and exhibited the best fit within the specified network of criterion constructs (i.e., depression, anxiety, negative affect, neuroticism, social desirability, and empathy). Notably, while these measures aligned best with predictions, correlations with theoretically distinct constructs (e.g., negative affect) were higher than predicted. The MPFI Flexibility scale generally exhibited high reliability, though it did not align well with predicted relationships with criterion measures. The CompACT and the PPFI tended to demonstrate poor reliability and poor validity with regard to the predicted nomological network. 

Results of this study provided evidence supporting the validity of the MPFI Inflexibility scale as well as the AAQ-II and its revision, the AAQ-3. It would likely be beneficial to consider altering the network of criterion measures to further evaluate how well each measure aligns with additional theoretically predicted relationships. Further, it is important to note that the pattern of results appeared to be consistent with previous literature suggesting that psychological flexibility and inflexibility may be related but distinct constructs (e.g., Stabbe et al., 2019), which could necessitate a slightly different nomological network. Overall, further evaluation of these measures of psychological (in)flexibility is important to further refine understanding of their respective reliability and validity as well as their utility in future clinical and research endeavors.