Validation and invariance testing of the Greek adaptation of the Acceptance and Action Questionnaire -II across clinical vs. nonclinical samples and sexes

The Acceptance and Action Questionnaire-II (AAQ-II) is a measure of experiential avoidance (EA), defined as the tendency to escape or avoid private psychological experiences, even when doing so is futile or interferes with valued actions (Hayes et al., 1996). Recent efforts have established the generalizability of this construct across different European cultures and languages and have established it as a deleterious psychopathological process. However, phenomenological differences of this construct between clinical vs. non-clinical samples have not yet been compared. The aim of the present study is to investigate the psychometrics of the Greek adaptation of the AAQ-II and examine measurement equivalence and scale invariance between different groups (sexes, clinical vs. nonclinical), before conclusions about the transdiagnosticity of this measure can be drawn. The total sample consisted of 274 (87 clinical outpatients; 75.8% female) Greek-speaking participants. Results suggest that the AAQ-II Greek translation has good psychometric properties, with high internal consistency, test-retest reliability, high correlations with similar constructs, and a unifactorial structure. Weak measurement invariance between clinical and non-clinical groups was established but scalar invariance failed. Regarding the sexes, invariance was established at all levels suggesting that EA can be considered a deleterious process irrespective of sex.