The Multidimensional Psychological Flexibility Inventory (MPFI): Discriminant validity of psychological flexibility with distress

The psychological flexibility model of behavior change underpins acceptance and commitment therapy (ACT). However, the measurement of psychological flexibility over the past 20 years has mostly hinged on the use of measures with poor discriminant validity and fuzzy boundaries with distress and negative emotionality. The current study analyzed the structure of psychological flexibility as assessed with the recently developed Multidimensional Psychological Flexibility Inventory (MPFI) and examined its link with distress. We used data from an online cross-sectional survey (N = 1542) which assessed psychological flexibility with the MPFI and the Acceptance and Action Questionnaire-II (AAQ-II), as well as anxiety, and depression. Exploratory and confirmatory factor analyses highlighted that the six psychological flexibility processes of the MPFI loaded on a psychological flexibility factor, while anxiety, depression and the AAQ-II loaded on a distress factor, supporting the discriminant validity of the MPFI in assessing psychological flexibility. Findings were consistent with those from prior studies which suggest that the AAQ-II is more of a measure of global distress than psychological inflexibility or by proxy, psychological flexibility. The 30-item MPFI psychological flexibility scale demonstrated good construct and discriminant validity. Overall, findings support psychological flexibility as a construct that is empirically distinct from distress.