Improving the structural validity of the QuickDASH questionnaire: Exploratory factor analysis and structural equation modelling in 1798 patients with carpal tunnel syndrome.

STUDY DESIGN: Retrospective cohort. BACKGROUND: The QuickDASH is a commonly used questionnaire for the assessment of carpal tunnel patients, although it is unclear whether the questionnaire has suitable structural validity PURPOSE: This study aimed to evaluate the structural validity of the QuickDASH patient-reported outcome measure (PROM), when used in CTS, through exploratory factor analysis (EFA) and structural equation modelling (SEM). METHODS: Between 2013 and 2019, we recorded preoperative QuickDASH scores of 1916 patients undergoing carpal tunnel decompressions at a single unit. One hundred and eighteen patients with incomplete datasets were excluded leaving a final study group of 1798 patients with complete data. EFA was undertaken using the R statistical computing environment. We then conducted SEM in a random sample of 200 patients. Model fit was assessed using the chi-square (χ2) test, comparative fit index (CFI), Tucker-Lewis index (TLI), root mean square error of approximation (RMSEA) and standardized root mean square residuals (SRMR). A second "validation" SEM analysis was undertaken by repeating the analysis with a separate sample of 200 randomly-selected patients. RESULTS: EFA revealed a 2-factor model: items 1-6 represented the first factor ("function") and items 9-11 measured a different factor ("symptoms"). SEM demonstrated excellent fit (χ2 p value 0.167, CFI 0.999, TLI 0.999, RMSEA 0.032, SRMR 0.046) and this was supported in our "validation" sample. CONCLUSIONS: This study demonstrates that the QuickDASH PROM measures 2 distinct factors in CTS. This is comparable with the findings of a previous EFA that assessed the full-length Disabilities of the Arm, Shoulder and Hand PROM in patients with Dupuytren's disease.