New insights into inequalities in life expectancy and mortality: evidence from an Individual-level Socio-Economic Index (ISEI) in Australia

Background
Socio-economic inequalities in life expectancy and mortality have received significant academic and policy attention in many high-income countries. Most studies to date have measured area-level inequalities either using a composite socio-economic index or individual-level inequalities using a single or limited variables (e.g. education, income). However, these approaches might underestimate life expectancy inequalities compared to a composite index of individual-level socioeconomic characteristics.

Methods
This study fills a major gap in evidence of life expectancy inequalities by analysing 2016 Population Census data linked at the individual level to death registration data from 2016 to 19 in Australia. We used Multiple Correspondence Analysis to construct an Individual-level Socio-Economic Index (ISEI) comprising variables representing education, income, marital status and whether living alone, housing tenure, migrant status, place of residence and neighbourhood socio-economic index. The ISEI was constructed separately for each sex and 10-year age group. Life expectancy at 25 and 65 years, partial life expectancy from 25 to 65 years and age-standardised and age-specific mortality rates were calculated and compared between ISEI percentiles (approximately 85,000 population each) and percentile groups.

Results
Life expectancy at age 25 years ranged from 43.2 (95% confidence intervals 42.8–43.6) years in the lowest (p1) ISEI percentile to 62.9 (62.5–63.4) years in the highest (p100) for males (gap of 19.7 years) and 51.7 (51.3–52.2) to 64.3 (64.0-64.8) years for females (gap of 12.6 years). The ISEI-life expectancy relationship was strong across all percentiles, with the gradient steepest in the lowest percentiles, flatter in middle deciles and slightly steeper in the highest percentiles. Partial life expectancy from 25 to 65 years had a steep gradient in the lowest ISEI percentiles but had a narrower total gap compared with life expectancy at 65 years. Age-standardised mortality rates (25–64 years) differed between p1 and p100 by a magnitude of 17.7 times for males and 11.8 times for females, with the largest disparities at 35–54 years.

Conclusions
This study shows substantial and concerning inequalities in life expectancy and mortality in Australia. By analysing these indicators with greater granularity than earlier studies by using a multidimensional socio-economic index, it shows wider disparities than previously and the important contribution of a wide range of social determinants.