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 (χ) 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 (χ 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.