Psychometric evaluation of the HIV symptom distress scale

Abstract

The objective of this article is to psychometrically validate the HIV symptom distress scale (SDS), an instrument that can be used to measure overall HIV symptom distress or clinically relevant groups of HIV symptoms. A secondary data analysis was conducted using the Collaborations in HIV Outcomes Research US Cohort (CHORUS). Inclusion criteria required study participants (N=5521) to have a valid baseline measure of the AIDS Clinical Trial Group Symptom Distress Module, with an SF-12 or SF-36 completed on the same day. Psychometric testing assessed unidimensionality, internal consistency, and factor structure using exploratory and confirmatory factor analysis, and structural equation modeling (SEM). Construct validity examined whether the new measure discriminates across clinical significance (CD4 and HIV viral load). Findings show that the SDS has high reliability (α=0.92), and SEM supports a correlated second-order factor model (physical and mental distress) with acceptable fit (GFI=0.88, AGFI=0.85, NFI=0.99, NNFI=0.99; RMSEA=0.06, [90% CI 0.06 – 0.06]; Satorra Bentler scaled, C ₂ =3274.20; p=0.0). Construct validity shows significant differences across categories for HIV-1 viral load (p<0.001) and CD4 (p<0.001). Differences in mean SDS scores exist across gender (p<0.001), race/ethnicity (p<0.05), and educational attainment (p<0.001). Hence, the HIV SDS is a reliable and valid instrument, which measures overall HIV symptoms or clinically relevant groups of symptoms.

Keywords:

• HIV symptom distress
• mental distress
• physical distress
• psychometric
• SF-12

Acknowledgements

We would like to thank scientists at GlaxoSmithKline for approving the secondary analysis of the CHORUS data-set; and we also thank Adriane Gelpi from Harvard University, Faculty of Arts and Sciences, for proofreading the final draft. Development of this manuscript was supported, in part, by awards to LGM from the National Institute of Health (#T32 MH19132, #T32MH067555 and L60-MD002421-01). Statistical support was provided to LGM, in part, at the Summer Institute for Applied Multi-Ethnic Research at the Inter-University Consortium for Political and Social Science Research, University of Michigan, Ann-Arbor. This project was funded by GlaxoSmithKline, and LGM received consultancy fees from Behavioral Science International LLC, GlaxoSmithKline and Pfizer during the study period.