The Psychological Inflexibility in Pain Scale (PIPS) - Statistical properties and model fit of an instrument to assess change processes in pain related disability

Recent developments within CBT have emphasized acceptance rather than control of pain and distress in treatments aimed at improving functioning and life quality, but there is still a lack of reliable and valid instruments to assess relevant processes in such interventions. The Psychological Inflexibility in Pain Scale (PIPS) was developed to assess target variables in exposure and acceptance oriented treatments. A preliminary validation study resulted in a two-factor solution with subscales for avoidance and cognitive fusion related to pain, showing satisfactory psychometric properties. This study sought to evaluate the instrument with 611 participants with whiplash associated disorders. Exploratory and confirmatory factor analyses supported a two-factor solution with 12 items which showed an acceptable model fit, adequate internal consistencies, and strong relations with criteria variables (e.g. disability and life satisfaction). The construct validity of the instrument was supported by high correlations with subscales from the Chronic Pain Acceptance Questionnaire (CPAQ) and the Tampa Scale of Kinesiophobia (TSK). Notably, hierarchical regression analyses illustrated that PIPS explained more variance than TSK in pain, disability, life satisfaction and depression. Furthermore, PIPS was found to mediate the relationship between e.g. pain and disability, suggesting the usefulness of PIPS as a process measure in treatments of people with chronic pain. Thus, it is argued that this 12-item version of PIPS may be used to explore the importance of psychological in/flexibility in chronic pain and to analyse processes of change in exposure based interventions, as well as for clinicians in tailoring interventions for patients with chronic debilitating pain.