Self-rated health (SRH) is an independent, strong predictor of morbidity and mortality. Socio-economic status (SES) is strongly associated with SRH. This study investigated the relationship between SES and SRH outcomes in a sample of patients with rheumatoid arthritis (RA) in Canada.
Both generic preference-based [Health Utilities Index Mark 3 (HUI3) and Short Form 6D (SF-6D)] and non-preference-based [disease-specific (Rheumatoid Arthritis Quality of Life, RAQoL) and a functional status (Health Assessment Questionnaire, HAQ)] SRH questionnaires were administered to 313 RA patients. Both proximate (education and annual household income) and contextual (neighbourhood income, education and unemployment) measures of SES were captured. Ordinary least squares (OLS) regression was used to adjust for RA severity while assessing the relationship between SRH and SES measures. Two-stage least-squares (TSLS) regression was used to determine if there was an inter-relationship between SES and SRH measures.
The sample was well distributed across RA severity and SES measures. Contextual and proximate measures of SES were poorly correlated. Lower levels of proximate SES measures (but not contextual) were associated with poorer SRH outcomes. The OLS regressions showed significant associations between the HUI3 and the SF-6D overall scores and the HAQ for self-reported income. The RAQoL did not differ significantly across SES. TSLS regression confirmed the finding that self-reported income was similarly associated with the SRH measures.
Even in a country with universal access to health-care, the impact of a chronic disease such as RA on SRH is associated with self-reported income. The finding that preference-based measures vary with income independently of RA severity could bias economic evaluation.