Objectives: The aim was to examine the responsiveness, presence of floor or ceiling effects, and minimal clinically important differences (MCIDs) for 2 new measures of pain-related catastrophizing and self-efficacy in individuals with chronic low back pain.
Methods: A total of 183 individuals with chronic low back pain recruited from physical therapy clinics in Thailand completed the Thai versions of the 6-item University of Washington Concerns About Pain scale (T-UW-CAP6) and 6-item University of Washington Pain-Related Self-Efficacy scale (T-UW-PRSE6) at baseline and at 4 weeks follow-up. Perceived change in low back symptom was assessed at 4 weeks using a 7-point measure of Global Perceived Effect (GPE). Responsiveness of the T-UW-CAP6 and the T-UW-PRSE6 scale scores were evaluated by computing the effect sizes and standardized response means for change over time, and examining these as a function of the GPE ratings. Floor and ceiling effects were examined by evaluating the score distributions. Scale core MCIDs were estimated by computing a half a SD and SE of measurement statistics for each scale.
Results: Responsiveness of the scales to pain treatment was supported by differences found in the mean change scores as a function of the treatment response categories. No significant floor or ceiling effects were found for either measure. Changes of 4.38 and 3.68 appeared to be the smallest change score perceived as clinical meaningful for the T-UW-CAP6 and T-UW-PRSE 6 scale scores, respectively.
Discussion: The T-UW-CAP6 and T-UW-PRSE6 demonstrated good ability to detect perceived changes over time in patients with chronic low back pain. The MCIDs values provide a benchmark for assessing individual improvement in this clinical context.
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