Introduction: To help researchers in multiple sclerosis (MS) take advantage of the measurement properties of the PROMIS Pain Interference instrument while maintaining continuity with previous research, we developed and tested a crosswalk table to transform Brief Pain Inventory pain interference scale (BPI-PI) scores to PROMIS-PI short form (PROMIS-PI SF) scores.
Methods: The BPI-PI and the PROMIS-PI SF were administered in two studies that included persons with MS. One sample of 369 participants served as a developmental calibration sample, and a separate sample of 360 served as a validation sample. The crosswalk development included dimensionality assessment, item-level parameter estimation, and assessment of accuracy. BPI-PI and PROMIS-PI T scores were obtained from participants' item responses, and using the crosswalk table, PROMIS-PI T scores were derived from responses to the BPI-PI items. Differences between observed and crosswalked T scores were compared in both samples.
Results: For BPI-PI summary scores ranging from 0 to 10, corresponding T scores ranged from 38.6 to 81.2. The mean difference between observed and crosswalked T scores was 0.51 (SD = 3.9) in the calibration sample and -1.47 (SD = 4.2) in the validation sample. Approximately 80 % of crosswalked scores in the calibration sample were within four score points of the observed PROMIS-PI SF scores, and 70 % were within four points in the validation sample. In both samples, the largest differences were at lower levels of the pain interference continuum.
Conclusions: Crosswalked pain interference scores adequately approximated observed PROMIS-PI SF scores in both the calibration and validation samples. MS researchers and clinicians interested in adopting the PROMIS instruments can use this table to transform BPI-PI scores to enable comparisons with other studies and to maintain continuity with previous research.