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.
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