Validation of single-factor structure and scoring protocol for the Health Assessment Questionnaire-Disability Index

Objective. The extensively used Health Assessment Questionnaire Disability Index (HAQ-DI) has been well received by the research and clinical community, notably because of its measurement strengths including reliability and stability of scores over time, utility in observational studies and clinical trials, predictive relationship with morbidity and mortality in rheumatoid arthritis (RA), and its translation for use in different countries. However, HAQ-DI scoring has not been validated. The purpose of this study was to examine the structural validity of the HAQ-DI and evaluate the latent factors underlying HAQ-DI scoring. Methods. This study used a cross-validation approach on a total of 278 patients with RA. Exploratory and confirmatory factor analyses were performed. Results. Results yielded a single-factor HAQ-DI score, which favored the current scoring system of the HAQ-DI. Additionally, modification indices suggested improved model fit with the secondary inclusion of correlated residual scores from a motor skills subdomain. Conclusion. The current study provides the first validation of the HAQ-DI scoring system as determined by its latent factor structure. In addition, the findings suggest some benefit from a secondary interpretation of the scores based on domains that measure motor skills.