Measuring pain phenomena after spinal cord injury: Development and psychometric properties of the SCI-QOL Pain Interference and Pain Behavior assessment tools

Objective: To develop modern patient-reported outcome measures that assess pain interference and pain behavior after spinal cord injury (SCI). Design: Grounded-theory based qualitative item development; large-scale item calibration field-testing; confirmatory factor analyses; graded response model item response theory analyses; statistical linking techniques to transform scores to the Patient Reported Outcome Measurement Information System (PROMIS) metric. Setting: Five SCI Model Systems centers and one Department of Veterans Affairs medical center in the United States. Participants: Adults with traumatic SCI. Interventions: N/A. Outcome Measures: Spinal Cord Injury - Quality of Life (SCI-QOL) Pain Interference item bank, SCI-QOL Pain Interference short form, and SCI-QOL Pain Behavior scale. Results: Seven hundred fifty-seven individuals with traumatic SCI completed 58 items addressing various aspects of pain. Items were then separated by whether they assessed pain interference or pain behavior, and poorly functioning items were removed. Confirmatory factor analyses confirmed that each set of items was unidimensional, and item response theory analyses were used to estimate slopes and thresholds for the items. Ultimately, 7 items (4 from PROMIS) comprised the Pain Behavior scale and 25 items (18 from PROMIS) comprised the Pain Interference item bank. Ten of these 25 items were selected to form the Pain Interference short form. Conclusions: The SCI-QOL Pain Interference item bank and the SCI-QOL Pain Behavior scale demonstrated robust psychometric properties. The Pain Interference item bank is available as a computer adaptive test or short form for research and clinical applications, and scores are transformed to the PROMIS metric.