Introduction: To enable clinicians to adapt treatment methods during therapy and to further refine ACT theory through research, we must be able to measure processes of change. Existing research has supported the psychometric quality of ACT questionnaires used within the general population and for those designed for individuals experiencing chronic pain. Correlation studies have demonstrated evidence for ACT questionnaire reliability (internal-consistency, test-retest reliability) and for aspects of construct validity (discriminant, convergent validity). However, studies using quantitative methodology (factor analysis or multiple regression) to assess validity do not tell us how individuals understand questionnaire items or whether they are interpreted as intended. No existing study provides a comprehensive, empirical investigation of this important aspect of construct validity; content validity.
Aim: The current study investigated whether commonly used ACT questionnaires captured their intended processes in individuals experiencing chronic pain; to explore content validity.
Method: The study was conducted in two parts: 1) to establish the most frequently used ACT measures within research and clinical practice; 2) the main study: assessing ACT questionnaire validity. Participants receiving ACT for chronic pain were recruited. Cognitive interviewing methodology investigated how individuals made sense of questionnaires as they completed them. A taxonomy of problem classification was used to objectively classify errors made in completing items.
Results: Logical, lexical, conceptually inconsistent and ‘response’ errors were found within each ACT measure assessed (CPAQ-8, PIPS and AAQ-II). Patterns of error making demonstrated how accurately the items were understood; a number of items were identified as the most problematic.
Discussion: Findings showing where problems lie in respondent understanding could influence how future research may evaluate processes occurring during treatment, thus refining ACT theory itself. The findings are also important for clinical practice as valid measures are needed to understand how therapy works, enabling clinicians to adapt treatment, targeting specific sub-processes, thus improving outcomes.
