Standardised mortality in Australia

The numbers of deaths increase, whilst mortality rates decline.

Why were the numbers of deaths in Australia higher in 2021 than in the previous year?

Three factors influence death counts in a population:

• Population size: a larger group is more likely to experience people dying.
• Age structure: mortality risks increase with age, so older populations have more deaths.
• Mortality rates within age groups: in age bands, these rates change in time and space.

Differences in these factors result in changes to the numbers of deaths.

Australia has a growing population, which is also getting older. At the start of the century, there were around 19m Australian residents, with a median age of 35. By September 2020, the residential population was about 25.7m people. The median age was also above 37 years.

Even with mortality rates declining, a growing and ageing population is overwhelming. That leads to increased numbers of deaths each year. Improvements in mortality rates are an insufficient counterbalance.

(Image: R Pubs)

What if we look at age-standardised mortality? This is a statistical procedure. First, collect death statistics by different age groups. Second, calculate crude mortality rates for each group: divide deaths by population estimates. Third, put those age-specific rates into a weighted average. The Australian Bureau of Statistics uses the Australian population in June 2001 here.

That standard population defines these weights. The index accounts for changes in both the population size and age structure.

For doctor-certified deaths, standardised mortality was lower in 2021 than the pre-pandemic years. These figures do not include deaths referred to a coroner. As the Australian Bureau of Statistics states:

The age-standardised death rate for 2021 was 431.0, which was below the historical average (459.0) but above the rate for 2020 (424.5).

(Image: R Pubs)

Mortality due to respiratory diseases was higher in 2021 than the previous year. Public health measures are a plausible reason for reduced respiratory illness.

Dementia, the second leading cause of death in Australia, had a higher rate than in 2020. Age-standardised rates due to dementia also exceeded the 2015–2019 average.

Other causes, like cancer and ischaemic heart disease, recorded lower rates in 2021. Mortality in different countries needs measured examination.

The code for the graphs is available on GitHub and R Pubs.