Measures of socioeconomic position are not consistently associated with ethnic differences in cardiovascular disease in Scotland: methods from the Scottish Health and Ethnicity Linkage Study (SHELS)

BACKGROUND: Ethnic health inequalities are substantial. One explanation relates to socioeconomic differences between groups. However, socioeconomic variables need to be comparable across ethnic groups as measures of socioeconomic position (SEP) and indicators of health outcomes. METHODS: We linked self-reported SEP and ethnicity data on 4.65 million individuals from the 2001 Scottish Census to hospital admission and mortality data for cardiovascular disease (CVD). We examined the direction, strength and linearity of association between eight individual, household and area socioeconomic measures and CVD in 10 ethnic groups and the impact of SEP adjustment. RESULTS: There was wide socioeconomic variation between groups. All eight measures showed consistent, positive associations with CVD in White populations, as did educational qualification in non-White ethnic groups. For other SEP measures, associations tended to be consistent with those of White groups though there were one or two exceptions in each non-White group. Multiple SEP adjustment had little effect on relative risk of CVD for most groups. Where it did, the effect varied in direction and magnitude (for example increasing adjusted risk by 23% in Indian men but attenuating it by 11% among Pakistani women). CONCLUSIONS: Across groups, SEP measures were inconsistently associated with CVD hospitalization or death, with effect size and direction of effect after adjustment varying across ethnic groups. We recommend that researchers systematically explore the effect of their choice of SEP indicators, using standard multivariate methods where appropriate, to demonstrate their cross-ethnic group validity as potential confounding variables for the specific groups and outcomes of interest.