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

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