Migration is actually slowing the rate of ageing of Australia’s population. I modelled how much fertility, mortality, overseas migration and interstate migration, all contribute to the overall change in the average age of a population.

Population ageing is measured by changes in the median age (the age at which half the population is older and half is younger) over time. For Australia, the median age is 37.2 years. The Northern Territory is the youngest state or territory with a a median age of 32.4 years and Tasmania is the oldest at 42 years.

In the model, births and deaths reduce the rate of ageing in the population. But the effects of migration can go either way.

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The impact of overseas migration on the average age of the population is dependent on the age and number of immigrants and emigrants compared with the average age of the population.

Between 2005 and 2015, Australia’s average age increased by 1.1 years from 37.5 years to 38.6 years. In the model, this was an increase of five weeks per year. In the absence of migration, Australia’s average age would have increased by 11 weeks per year.

This is because over the period, the number of overseas arrivals was almost double that of overseas departures and, on average, they were younger. This provides evidence that policy intervention, such as the shift to a skilled migration program and the increase in the number of international students, can influence the rate of population ageing.

Why Tasmania is the oldest

Overseas migration also contributed to a slowing of the rate of ageing for Tasmania. However, between 2005 and 2015, Tasmania’s average age increased from 38.6 years to 41 years (an increase of 2.4 years). This suggests other factors are at play in increasing the average age of the population, particularly when compared with the considerably lower change in Australia’s average age.

The difference in ageing between Australia and Tasmania of five weeks per year is largely explained by interstate migration. The number of interstate movements to and from Tasmania was around five times that of overseas movements.

While interstate arrivals were younger than the average Tasmanian, those leaving the state were even younger, contributing to increasing the average age of Tasmanians over time.

Essentially, in the absence of interstate migration, the rate of ageing in Tasmania would have slowed to an average of seven weeks per year, more comparable with Australia’s rate of ageing.

What this means for our future

The model’s findings confirm that as differences between fertility and mortality levels within a nation are usually small, it is migration, overseas and interstate, which is predominantly responsible for different changes in the average age of the nation.

National policy initiatives, such as the shift to a skilled migration program, and the increased level of international students have been effective in slowing the rate of population ageing for Australia, but not necessarily for regions like Tasmania.

Until now, governments have used “one-size-fits-all” solutions or those adopted from other places to deal with population ageing. These approaches fail to capture the diversity of population change within a nation.

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What is needed is local policies, developed and applied in situ, to meet the needs, strengths, challenges and opportunities of a region.Newfoundland and Labrador in Canada and Tasmania have both employed policies that are based on local areas. In Tasmania, the strategy focuses on creating jobs, migration strategies for those living interstate and overseas and the liveability of the place.

Understanding how and why populations change can effectively contribute to planning and investment in age-appropriate infrastructure, services and amenities.

Lisa Denny does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.