An observational study of intergenerational sex differences in mortality in Aotearoa New Zealand

Internationally, there are observable sex differentials in mortality in many countries, most notably in affluent countries, with women living longer than men. To understand if this is also the case in Aotearoa New Zealand (NZ), we visualise the precise nature and evolution of sex differentials in mortality by age over time, within a wider context of increasing life expectancy and falling mortality. This allows us to determine if NZ mirrors other affluent countries in having a male/female inequality in mortality, and how the inequality has evolved over several generations in NZ. We use newly available single-year mortality data by sex in NZ to visualise and analyse the sex differentials in mortality using an observational study design. Sex and age-specific mortality data were obtained from the human mortality database from 1948 to 2021 for NZ. The data were then processed to create a smoothed data series using a geometric mean of those two years older and younger as well as aggregating the single-year age groups over 90 into a single category due to small numbers. The processed data was then visualised using a lexis diagram. There are clear patterns of elevated mortality ratios at younger ages (18-30) for males compared to females. The relative difference in mortality inequality between the sexes grew between 1950 and 1980 in NZ, before converging between 2000 and 2020. There is a consistent gap of at least 3 years in life expectancy across the study period by sex. Particularly striking is the longstanding nature of this inequality in mortality by sex in NZ and the relative lack of focus from policymakers. This focus on one country, NZ, allows examination of this specific context to understand how policy changes may have exacerbated or ameliorated trends in male/female mortality inequality.