Age–social stratification designs had a negligible impact on income–mortality associations

Abstract

Objectives Age–social stratification has been used to offset socioeconomic status (SES) misclassification due to cohort effects. This study was to evaluate whether age–income stratification designs generate comparable income–mortality associations as those whose income rankings are based on absolute thresholds. Study Design and Setting Using self-reported income as our SES variable, and mortality as our outcome measure, the impact of age–social stratification was examined in two distinct cohorts: one with acute myocardial infarction (AMI) ( n = 3,138), and the second free of cardiovascular disease ( n = 15,115). Age-adjusted income–mortality associations were compared between age–social stratification techniques, which used “age-relative” income thresholds and “absolute” income thresholds whose ranks were independent of patient age. Results In both cohorts, crude mortality inversely correlated with age and income. Techniques using “age-relative” income thresholds yielded similar adjusted odds ratio for mortality as did those that used “absolute” income threshold methods (differences in adjusted odds ratios [±95% confidence interval (CI)] between “absolute” and “age-relative” classifications for highest vs. lowest income tertiles: −0.05 [−0.24, 0.12] among patients with AMI and 0.05 [−0.03, 0.13] among patients without cardiovascular disease). Conclusion More complex designs incorporating age–social stratification techniques generate similar income–mortality associations as more simplified approaches, which classified SES using absolute income thresholds.