The interpretation of change score of the pain disability index after vocational rehabilitation is baseline dependent

Abstract

BackgroundThe Pain Disability Index (PDI) is a widely-used instrument to measure pain-related disability. The aim of this study was to assess the responsiveness and interpretation of change score of the PDI in patients with chronic musculoskeletal pain (CMP) at discharge of vocational rehabilitation.MethodsRetrospective data of patients with CMP who attended vocational rehabilitation between 2014 and 2017 was used. The anchor-based method was used to assess the responsiveness of the total sample and of PDI baseline quartile groups. A receiver operating characteristic curve was performed, including Area Under the Curve (AUC) and Minimal Important Change (MIC).ResultsThe PDI showed responsive to detect clinically relevant changes in pain-related disability at discharge of vocational rehabilitation (AUC 0.79). A PDI change score of 13 points (MIC 12.5) can be considered as a real change in pain-related disability for the total study sample, and a PDI change score of 7–20 points can be considered as a real change in pain-related disability for PDI lowest and highest baseline quartile scores.ConclusionThe PDI is responsive in patients with CMP at discharge of vocational rehabilitation. The interpretation of change score depends on PDI baseline score. Patients with a PDI baseline score of ≤27 should decrease minimal 7 points, patients with a baseline score between 28 and 42 should decrease minimal 15 points, and patients with a baseline score ≥ 43 should decrease minimal 20 points.

Methodological and interpretive concerns about Beemster et al.’s article ‘The interpretation of change score of the pain disability index after vocational rehabilitation is baseline dependent’: a letter to the editor

“…Since they did not perform their own test-retest analysis, their ICC was derived from a study of Soer et al [4], who extensively validated the PDI in three groups of patients with musculoskeletal pain. Beemster et al state that this study's sample was similar to their own [1]. However, comparison of the descriptive statistics does not bear this out.…”

“…This mixed population (n = 845) had a mean baseline PDI score of 37.6 with a SD of 14.6 (personal communication with Soer R.). In contrast, Beemster et al found a baseline PDI score of 34.7 with a SD of 11.7 in their population of patients with CMP attending vocational rehabilitation [1]. These SDs show the former population to be more heterogeneous than the latter.…”

“…The second problem with the study is the way the standard error of measurement (SEM) has been calculated. The authors use a formula of debatable validity, SEM = SD √(1-ICC) [1] (where SD is the standard deviation and ICC is the intraclass correlation coefficient). Since they did not perform their own test-retest analysis, their ICC was derived from a study of Soer et al [4], who extensively validated the PDI in three groups of patients with musculoskeletal pain.…”

The (cost-)effectiveness and cost-utility of a novel integrative care initiative for patients with chronic musculoskeletal pain: the pragmatic trial protocol of Network Pain Rehabilitation Limburg

“…Scores from the individual items are summed to a total (0-70). The minimal important change is 13 points for patients with CMP [41]. The Dutch version of the PDI has proven internal consistency and test-retest reliability [42].…”

The (cost-)effectiveness and cost-utility of a novel integrative care initiative for patients with chronic musculoskeletal pain: the pragmatic trial protocol of Network Pain Rehabilitation Limburg

“…Scores from the individual items are summed to a total (0-70). The minimal important change is 13 points for patients with CMP(42). The Dutch version of the PDI has proven internal consistency and test-retest reliability(43).…”