Abstract
BackgroundThe association between lower socioeconomic status and poorer health outcomes has been observed using both individual-level and aggregate-level measures of income and education. While both are predictive of health outcomes, previous research indicates poor agreement between individual-level and aggregate-level measures. The purpose of this study was to determine the level of agreement between aggregate-level and individual-level measures of income and education among three distinct patient groups, specifically asthma, diabetes, and rheumatoid patients.MethodsIndividual-level measures of annual household income and education were derived from three separate surveys conducted among patients with asthma (n = 359), diabetes (n = 281) and rheumatoid arthritis (n = 275). Aggregate-level measures of income and education were derived from the 2001 Canadian census, including both census tract-and dissemination area-level measures. Cross-tabulations of individual-level income by aggregate-level income were used to determine the percentage of income classifications in agreement. The kappa statistic (simple and weighted), Spearman's rank correlations, and intra-class correlation coefficient (ICC) were also calculated. Individual-level and aggregate-level education was compared using Chi-Square tests within patient groups. Point biserial correlation coefficients between individual-level and aggregate-level education were computed.ResultsIndividual-level income was poorly correlated with aggregate-level measures, which provided the worst estimations of income among patients in the lowest income category at the individual-level. Both aggregate-level measures were best at approximating individual-level income in patients with diabetes, in whom aggregate-level estimates were only significantly different from individual-level measures for patients in the lowest income category. Among asthma patients, the proportion of patients classified by aggregate-level measures as having a university degree was significantly lower than that classified by individual-level measures. Among diabetes and rheumatoid arthritis patients, differences between aggregate and individual-level measures of education were not significant.ConclusionsAgreement between individual-level and aggregate-level measures of socioeconomic status may depend on the patient group as well as patient income. Research is needed to characterize differences between patient groups and help guide the choice of measures of socioeconomic status.
Highlights
The association between lower socioeconomic status and poorer health outcomes has been observed using both individual-level and aggregate-level measures of income and education
Individual-level household income was highest among patients with diabetes mellitus (DM), followed by patients with asthma and rheumatoid arthritis (RA), respectively (p < 0.0001, with all pairwise comparisons p < 0.0001)
There were no significant differences in the proportions of patients classed by census tract (CT) or dissemination area (DA) as having a university degree between the patient groups
Summary
The association between lower socioeconomic status and poorer health outcomes has been observed using both individual-level and aggregate-level measures of income and education. In Canada, studies aimed at quantifying the relationship between individual-level SES measurements and aggregates derived from Canadian census data have generally indicated poor agreement This finding is consistent across studies using individual-level measures derived from self-report [15], from structured interviews [16], and from public health insurance data [17,18]. These studies indicate that aggregate measures from the Canadian census function to mask variation in individuallevel measures, the latter being more sensitive to poverty and poor health outcomes. Studies using US census data further suggest that aggregate-level SES measures reflect a construct distinct from individual-level ones [19,20]
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