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.

Figure 1

Path Diagram for the One-Factor Model (Polychoric Correlation)

Figure 2

Two-Factor Model (Polychoric Correlation)