Responsiveness and minimal important change of the NeckPix© in subjects with chronic neck pain undergoing rehabilitation

Purpose: The NeckPix© is a simple and rapid means of measuring the beliefs of subjects with chronic neck pain concerning pain-related fears of a specific set of activities of daily living. The original version showed satisfactory psychometric properties. This observational study is aimed at evaluating its responsiveness and minimal important changes (MICs) in subjects with chronic neck pain. Methods: At the beginning, at the end of an 8-week rehabilitation programme as well as at the one-year follow-up, 153 subjects completed the NeckPix©. After the programme and at follow-up, subjects and physiotherapists also completed the global perceived effect (GPE) scale, which was divided to produce a dichotomous outcome. Responsiveness was calculated by distribution [effect size (ES); standardised response mean (SRM)] and anchor-based methods [receiver-operating characteristics (ROC) curves; correlations between change scores of the NeckPix© and GPEs]. ROC curves were also used to compute MICs. Results: The ES ranged from 0.95 to 1.26 and the SRM from 0.84 to 0.98 at post-treatment and follow-up based on subjects’ and physiotherapists’ perspective. The ROC analyses revealed AUCs of 0.89 and 0.97 at post-treatment and follow-up, respectively; MICs (sensitivity; specificity) were of 6 (0.82; 0.88) and 8 (0.80; 0.92) at post-treatment and of 8 (0.95; 0.90 based on subjects and 0.95; 0.92 based on physiotherapists perspective) at follow-up. The correlations between change scores of the NeckPix© and GPEs ranged from −0.69 to −0.82. Conclusions: The NeckPix© was sensitive in detecting clinical changes in subjects with chronic neck pain undergoing rehabilitation. We recommend taking the MICs provided into account when assessing subjects’ improvement or planning studies in this clinical context.