Gloster, A. T., Klotsche, J., Chacker, S., Hummel, K., & Hoyer, J. (2011). Assessing psychological flexibility: What does it add above and beyond existing constructs? Psychological Assessment, 23, 970-982.
The construct of psychological flexibility (PF) is a central concept in acceptance and commitment
therapy. It is defined as the process of contacting the present moment fully as a conscious human being
and persisting in or changing behavior in the service of chosen values. PF is hypothesized to be an
important aspect of healthy psychological functioning. Despite its potential importance, the distinctness
of PF from other constructs has not been adequately demonstrated, and psychometric evaluations of
measures designed to assess it are limited. This study aimed at extending current knowledge about PF by
examining the construct in 2 help-seeking samples, including panic disorder with agoraphobia (n = 368),
clinically relevant social phobia (n = 209), and 2 nonclinical samples including students (n = 495) and
individuals visiting an employment office (n = 95). Results across all samples indicate that PF, as
measured by the Acceptance and Action Questionnaire (2nd version; AAQ–II), is a unitary construct with
a 1 factor model. PF correlated with other variables largely consistent with predictions, differentiated
patients from healthy controls, and showed preliminary indications of treatment sensitivity. Incremental
validity was partially demonstrated, especially for indices of functioning. Surprisingly, PF also explained
unique variance above more established measures for some indices of symptomatology. Results suggest
that PF adds some incremental clinical validity, yet further and more stringent tests are required to fully
elucidate its strengths and limitations.