The Psychological Inflexibility in Pain Scale (PIPS) Exploration of Psychometric Properties in a Heterogeneous Chronic Pain Sample

Psychological flexibility receives increasing attention as the overarching process in Acceptance and Commitment Therapy (ACT). This study investigates the psychometric properties of the Psychological Inflexibility in Pain Scale (PIPS), measuring "avoidance" and "cognitive fusion" with pain, in a heterogeneous clinical sample of 428 chronic pain patients from four rehabilitation centers. Furthermore, the relationship between the PIPS and mindfulness (Five Facet Mindfulness Questionnaire, FFMQ) as a theoretically related measure within ACT is explored. Confirmatory factor analyses replicated acceptable/good model fit and internal consistencies. In a subsample from two rehabilitation centers (n = 237), the PIPS showed moderate to high relationships with aspects of mindfulness, pain interference in daily life, pain disability and mental health, and small relationships with pain intensity and physical functioning. The avoidance subscale explained additional variance in outcome variables beyond the FFMQ, ranging from 4.5 to 15.8%. Outcomes support the psychometric properties of the PIPS in a heterogeneous chronic pain sample. The PIPS and FFMQ measure slightly overlapping, but distinct constructs, and can be used complementary to assess a broad range of processes within ACT. Potential problems with the cognitive fusion subscale are acknowledged for future research.