The Health Assessment Questionnaire Disability Index is a valid measure of physical function in gout

Area of Science:

• Rheumatology
• Health Outcomes Research
• Psychometrics

Background:

• Gout is a common inflammatory arthritis causing significant physical disability.
• Existing disability instruments lack specific validation for gout patients.
• The Health Assessment Questionnaire Disability Index (HAQ-DI) is a widely used measure of physical function.

Purpose of the Study:

• To assess the construct validity of the HAQ-DI in a gout population.
• To evaluate the internal validity of the HAQ-DI using Rasch analysis.
• To determine if HAQ-DI is a suitable instrument for measuring disability in gout.

Main Methods:

• Observational cohort study involving two groups of gout patients (n=20, n=53).
• Correlation of clinical and functional measures with HAQ-DI scores.
• Rasch analysis applied to assess the internal validity of summated HAQ-DI scores.

Main Results:

• HAQ-DI demonstrated good construct and internal validity in gout patients.
• Rasch analysis confirmed internal validity, with improved model fit after rescoring items.
• HAQ-DI scores correlated highly with clinical indices and physical function measures.
• A significant relationship was found between days of sick leave and HAQ-DI scores (r2=0.44, p<0.001).

Conclusions:

• The HAQ-DI is a valid tool for assessing physical disability in gout.
• A modified scoring approach for the HAQ-DI enhances its fit with the Rasch measurement model.
• Findings support the use of HAQ-DI in clinical practice and research for gout patients.