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The Health Assessment Questionnaire Disability Index is a valid measure of physical function in gout
W J Taylor1, K Colvine, K Gregory
1Department of Medicine, University of Otago, Wellington, New Zealand. will.taylor@otago.ac.nz
Insights
The Health Assessment Questionnaire Disability Index (HAQ-DI) is valid for measuring disability in gout patients. Modifying its scoring improves accuracy, showing a strong link between HAQ-DI and sick leave days.
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.
Objective:
There are no disability instruments that have specifically been validated for gout. The aim of this study was to determine the construct validity of the Health Assessment Questionnaire Disability Index (HAQ-DI) in gout and the internal validity using Rasch analysis.
Methods:
An observational cohort study of two groups of clinic patients with gout (n=20, n=53), in which clinical and functional measures were correlated with HAQ-DI scores. Rasch analysis was used to determine the internal validity of summated scores as a measure of physical disability.
Results:
The HAQ-DI items fitted a Rasch measurement model, confirming internal validity of the scale, although there was evidence of disordered thresholds and rescoring items as a 3-option response rather than a 4-option response improved model fit and resolved the disordered thresholds. HAQ-DI scores showed a bimodal distribution and evidence of floor effects. Clinical indices correlated highly with HAQ-DI scores in gout patients, particularly other measures of physical function. A strong relationship between days of sick leave and HAQ-DI was observed in gout patients (r2=0.44, p<0.001).
Conclusions:
It is concluded that HAQ-DI has good construct and internal validity in gout but a modified scoring approach better fits a Rasch model.
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