Validity and reliability of the Gout Impact Scale in a multi-ethnic Asian population.

Abstract

The emphasis on capturing patient-reported outcomes (PRO) is increasing, but gout-specific PRO are lacking. We evaluated the reliability and validity of the 24-item Gout Impact Scale (GIS) of the Gout Assessment Questionnaire 2.0 (GAQ2.0) in a multi-ethnic Asian population. Participants with gout in an academic medical center in Singapore completed the GIS which comprises five scales. Confirmatory factor analyses (CFA) were performed. Known-groups validity, divergent validity and internal consistency were evaluated. We analyzed data of 267 participants (mean [SD] age 52.2 [16.08] years, 92.1% men and 76.0% Chinese). CFA based on the original GIS factor structure had good model fit based on Tucker-Lewis Index (TLI) of 0.946 but not when based on Root Mean Square Error Of Approximation (RMSEA), which was 0.123 (90% CI: 0.116-0.130). Internal consistency of GIS exceeded 0.7 in all except one scale, consistent with previous studies. Hypotheses related to known-groups validity were largely supported. Scores were significantly higher (ie greater impact) for participants reporting at least some problem on the EQ-5D-3L anxiety/ depression item across all GIS scales. Correlations between RAND-36 Physical Functioning (PF) scale and all five scales in the GIS were poor (Spearman rank correlation coefficients: -0.2355 to 0.0426), implying that GIS does not measure impact of gout on physical health. The GIS is valid and reliable for assessing gout-specific psychosocial functioning in a multi-ethnic Asian population.