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Measured Test-Retest Reliability for Patients With Psoriatic Arthritis

Test-retest reliability for Health Assessment Questionnaire–Disability Index and 36-item Short Form Health Survey physical functioning domain in patients with psoriatic arthritis was judged to be good and reasonable, respectively.

The Health Assessment Questionnaire–Disability Index (HAQ-DI) and 36-item Short Form Health Survey physical functioning domain (SF-36 PF) had a reasonable test-retest reliability for patients with psoriatic arthritis (PsA), according to a study published in The Journal of Rheumatology.1

“Reliability is a basic and essential measurement property for an instrument to be an accurate representation of the participant’s performance rather than due to contextual factors of the testing session, such as environmental, psychological, or methodological processes,” investigators stated. “Physical function (PF) is one of the core domains to be measured in every randomized controlled trial and longitudinal study in psoriatic arthritis (PsA).”

Of the 2 datasets identified, 1 evaluated test-retest reliability for both HAQ-DI and SF-36 PF and the other analyzed HAQ-DI alone. All were analyzed using the Outcome Measures in Rheumatology (OMERACT) Filter 2.1 methodology requirements. In the first dataset, 31 patients (77% male) with stable disease who were not receiving medication change were given HAQ-DI and SF-36 PF assessments both at baseline and Week 1. In the second dataset, HAQ-DI was used as a comparator tool for 38 patients (44.7% male) who did not need any medication change and data was collected at baseline and Week 2.

For each dataset, the intraclass correlation coefficient (ICC) and Spearman rank correlations between scores were calculated for both HAQ-DI and SF-36 PF to ensure test-retest reliability.

Both datasets were eligible for HAQ-DI and SF-36 PF and quality was classified per the OMERACT checklist. In the first study, the mean age was 54 years and the duration of illness was 5.7 years. Mean HAQ-DI at baseline and the 1-week follow-up were 0.54 and 0.52, respectively. The ICC of HAQ-DI between baseline and 1-week follow-up was good (0.90, 95% CI 0.79–0.95) and Bland-Altman plots showed no difference between baseline and Week 1 scores.

SF-36 PF scores at baseline and 1-week were 63.6 and 66.7, respectively. The ICC was excellent (0.96, 95% CI 0.92–0.98) and Spearman ρ was 0.95 (P < 0.01). Bland-Altman also showed no difference between the 2 assessments.

In the second study, HAQ-DI was 0.38 at baseline and 0.35 at Week 2. The ICC for HAQ-DI was categorized as excellent (0.94, 95% CI 0.89–0.97) and Spearman ρ was 0.83 (P < 0.001). The Bland-Altman assessment showed no difference between both scores and adequacy of test-retest reliability was rated as adequate.

As both datasets were of good quality and adequate performance, the test-retest reliability for HAQ-DI was rated GREEN. Regarding the SF-36 PF assessments, the test-retest reliability was rated AMBER.

“We have demonstrated test-retest reliability for HAQ-DI and SF-36 PF in PsA, which was judged to be good and reasonable, respectively,” investigators concluded.


Leung YY, Tillett W, Hojgaard P, et al. Test-retest Reliability for HAQ-DI and SF-36 PF for the Measurement of Physical Function in Psoriatic Arthritis. J Rheumatol. 2021;48(10):1547-1551. doi:10.3899/jrheum.210175