Validity and reliability of the Short Form 36 Health Surveys (SF-36) among patients with spondyloarthritis in Singapore.

The Short Form 36 Health Survey (SF-36) is a popular health-related quality of life (HrQoL) tool. However, few studies have assessed its psychometric properties in patients with spondyloarthritis (SpA). We therefore aimed to assess the reliability and validity of the SF-36 in patients with SpA in Singapore. Cross-sectional data from a registry of 196 SpA patients recruited from a dedicated tertiary referral clinic in Singapore from 2011 to 2014 was used. Analyses were guided by the COnsensus-based Standards for the selection of health Measurement INstruments framework. Internal consistency reliability was assessed using Cronbach's alpha. Construct validity was assessed through 33 a priori hypotheses by correlations of the eight subscales and two summary scores of SF-36 with other health outcomes. Known-group construct validity was assessed by comparison of the means of the subscales and summary scores of the SF-36 of SpA patients and the general population of Singapore using student's t tests. Among 196 patients (155 males (79.0 %), median (range) age: 36 (17-70), 166 Chinese (84.6 %)), SF-36 scales showed high internal consistency ranging from 0.88 to 0.90. Convergent construct validity was supported as shown by fulfillment of all hypotheses. Divergent construct validity was supported, as SF-36 MCS was not associated with PGA, pain and HAQ. Known-group construct validity showed SpA patients had lower scores of 3.8-12.5 when compared to the general population at p < 0.001. This study supports the SF-36 as a valid and reliable measure of HrQoL for use in patients with SpA at a single time point.

Validity and reliability of the Health Assessment Questionnaire among patients with spondyloarthritis in Singapore.

AIM: The Health Assessment Questionnaire (HAQ) is a popular tool used to measure disability. Few studies have assessed its psychometric properties in patients with spondyloarthritis (SpA). We therefore aimed to assess the reliability and validity of the HAQ in patients with SpA in Singapore. METHOD: Cross-sectional data from a registry of 196 patients with SpA recruited from a dedicated tertiary referral clinic in Singapore from 2011 to 2014 was used. Analyses were guided by the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) framework. Internal consistency reliability was assessed using Cronbach's alpha. Convergent construct validity was assessed by 30 a priori hypotheses through correlation of the summary score and the eight domain scores of the HAQ with other health outcome measures: Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Global Score (BASG), pain, Patient's Global Assessment (PGA) and Short Form-36 Health Survey (SF-36). Divergent construct validity was assessed by poor correlation of HAQ with SF-36 Mental component score (MCS). RESULTS: Among 196 patients (155 males [79.1%] median [range] age: 36 [17-70]; 166 Chinese [84.7%]), the HAQ showed a high internal consistency of 0.78-0.84. Convergent validity was supported by achieving 26 out of the 30 a priori hypotheses. Divergent validity was also established- correlation of SF-36 MCS with seven domains and summary scores of the HAQ were not statistically significant. CONCLUSION: This study supports the HAQ as a valid and reliable measure of disability for use in patients with SpA.