The Psychological Inflexibility in Pain Scale (PIPS): Validity and Reliability of the Japanese Version for Chronic Low Back Pain and Knee Pain.

Purpose The aim of this study was to translate the Psychological Inflexibility in Pain Scale Japanese version (PIPS-J) and inspect its validity and reliability in older patients with chronic low back pain and knee pain. Materials and Methods The PIPS was translated into Japanese by a bilingual linguistic expert and three researchers and administered to 120 outpatients with low back pain and knee pain (61.7% women, age 73.8±7.8 years). Construct validity and criterion validity were evaluated using confirmatory factor analysis and the correlations with the Acceptance and Action Questionnaire-II Japanese version (AAQ-II-J) and the Cognitive Fusion Questionnaire Japanese version (CFQ-J), respectively. Internal consistency using Cronbach’s alpha and test–retest reliability (n=43) were also examined. Results Of all, 78.3% had low back pain, 55.6% had knee pain, and 44.2% both. The confirmatory factor analysis reproduced the original PIPS structure with two factors and indicated good model fit (GFI = 0.915, CFI = 0.970, RMSEA = 0.060). All items’ standardized regression weights ranged from 0.35 to 0.80. Criterion validity was shown by correlations of r = 0.58 for PIPS-J pain avoidance with the AAQ-II-J, and r = 0.45 between PIPS-J cognitive fusion and the CFQ-J. Cronbach’s alpha for the PIPS-J total score was α=0.85 (pain avoidance: 0.87; cognitive fusion: 0.68). The test–retest correlation for all 12 items was r = 0.54 (pain avoidance: 0.48; cognitive fusion: 0.54). Conclusion Although a less relevant item was found on each of subscales, the PIPS-J appear to be fairly valid and reliable to evaluate psychological inflexibility in chronic pain among Japanese older adults.