Socioeconomic inequalities in mortality by cause in Australia: a multiple-cause weighting approach

Background

Socioeconomic inequalities in mortality are most commonly assessed using the underlying cause of death (UC), ignoring multimorbidity at death despite its wide socioeconomic inequalities. We examined the impact of multiple-cause weighting (MCW) to measure causes of death, rather than UC, on socioeconomic inequalities in cause-specific mortality in Australia.

Methods

We analysed national mortality data for 2016-2019 linked to the 2016 Census in the Person-Level Integrated Data Asset, by age (25-64, 65+) and sex. Socioeconomic position was measured using education, equivalised household income and area-level Index of Relative Socio-economic Advantage and Disadvantage. Across 17 leading causes, we compared mortality rates measured using UC with MCW, weighting 50% of each death to the UC and 50% equally across conditions recorded in Part II of the death certificate. Inequalities in mortality rates were measured using the Relative Index of Inequality (RII) and Slope Index of Inequality (SII). MCW age-standardised mortality rates and SIIs were decomposed into UC and Part II components.

Results

Relative inequalities in mortality were generally wider at ages 25-64 than at ages 65+. Across the 17 causes, RII differences between UC and MCW were generally modest. For causes more often recorded in Part II, RIIs were similar between UC and MCW at ages 65+, whereas at ages 25-64 RIIs were lower under MCW; for renal failure, the education RII was 8.1 (MCW) vs 16.6 (UC) in men and 8.6 vs 12.0 in women. The Part II contribution to absolute inequality was substantial for diabetes, hypertension and renal failure, whereas for most causes the UC component contributed more than Part II.

Conclusions

Using UC alone does not fully capture cause-specific socioeconomic inequalities in mortality compared with MCW. This is especially relevant for chronic diseases that typically co-occur with other conditions, such as diabetes and renal failure, that demonstrate large inequalities.

Key messages

• The underlying cause of death approach underestimates absolute inequalities for causes of death that commonly co-occur with other conditions, such as diabetes and renal failure.

• Across 17 causes, differences in relative inequality between the underlying cause and multiple-cause weighting approaches were generally modest and smaller at ages 65+ than at ages 25-64.