Comprehensive assessment of Acceptance and Commitment Therapy processes (CompACT): Measure refinement and study of measurement invariance across Portuguese and UK samples

The need for a transnational validation is imperative at the stage of development of the CompACT, a self-report measure of psychological flexibility. This study aimed to translate, validate and test the factor structure of the Portuguese version of the CompACT and to conduct a measurement invariance analysis comparing the scale’s performance in Portuguese and UK samples. Results from an Exploratory Factor Analysis demonstrated that the Portuguese version of the CompACT statistically performed better without 5 items from the Openness to Experience subscale. The 18-item Portuguese-adapted CompACT presented significant correlations in the expected directions and with the expected magnitudes with AAQ-II, CFQ-7, MAAS, CAQ-8, and DASS-21. Partial metric invariance was demonstrated between the Portuguese-adapted 18-item CompACT and the original CompACT in a UK sample. The non-correspondence between responses to these versions may be due to differences between the Portuguese and British cultures. This study contributes with the adaptation of the original CompACT to the Portuguese language and with the refinement of this instrument to an 18-item measure of psychological flexibility, that appears to be adequate for use in Portuguese samples. The lack of complete metric invariance of the CompACT found across the Portuguese and UK samples highlights the importance of psychometrically analyzing psychological instruments before use in cultural contexts distinct from the one targeted in the measure’s original validation study