Comparative responsiveness of generic versus disease-specific and weighted versus unweighted health status measures in carpal tunnel syndrome

Abstract

Objectives: The authors evaluated the relative responsiveness to change of generic versus disease-specific and unweighted versus weighted health status measures in carpal tunnel syndrome (CTS).

Methods: Data were obtained from 196 subjects followed in a prospective community-based cohort study in Maine who underwent carpal tunnel release (The Maine Carpal Tunnel Syndrome Study). Patients were evaluated before and 6 months after surgery. The disease-specific, unweighted severity score was derived from the validated Carpal Tunnel Syndrome Assessment Questionnaire. Patients were asked to rate the importance of each symptom included in the severity score. Each severity question was weighted by its importance, creating a disease-specific weighted score. Generic instruments were the SF-36, SF-12, and a Quality of Life Rating Scale. Sensitivity to change was calculated with the standardized response mean (SRM, mean change/standard deviation of change) as well as the effect size (ES, mean change/standard deviation of baseline values). The ability of the instruments to distinguish clinically important differences was assessed by correlating the changes in scores with global ratings on satisfaction and perceived improvement as external criteria.

Results: The disease-specific weighted score (SRM: 1.56, ES: 1.99) was more responsive than the unweighted score (SRM: 1.36, ES: 1.57). The Quality of Life Rating Scale, SF-36, and SF-12 subscales were less sensitive to change, with standardized response means and effect sizes that ranged from -0.23 to 0.88. The ability to distinguish clinically important differences was higher for the two disease-specific scales. The coefficients of correlation with the external criteria ranged from 0.50 to 0.56 for the unweighted score and 0.56 to 0.62 for the weighted score and were significantly stronger than the correlations between external measures and the most responsive subscale of the SF-36 (Bodily Pain subscale, r = 0.36). The SF-12 health survey performed as well as the SF-36 in term of responsiveness and ability to distinguish clinically important change.

Conclusions: Disease-specific measures were superior to generic measures in capturing clinical change after carpal tunnel release, and a weighted score was slightly more responsive than the unweighted score. The SF-12 showed comparable psychometric properties compared with the longer 36-item Short-Form Survey.