Saturday, 9 September 2017

The relative (un)certainty of subnational population decline

Over the three years up to March of this year, I was involved in a Marsden Fund project led by Natalie Jackson, looking at subnational depopulation in New Zealand. That is, among other things we were trying to explain why some areas of New Zealand have been declining in population over time, and continue to do so. The outputs of that project have been summarised in a recent issue of the journal Policy Quarterly.

My contribution to that issue of Policy Quarterly (from pages 55-60) is entitled "The relative (un)certainty of subnational population decline", and looks at how certain (or uncertain) population decline is for different territorial authorities in New Zealand. However, the article has a broader purpose, and is worth reading because it outlines some of the key points that decision-makers need to understand about population projections, especially in terms of their uncertainty. If you know nothing about population projections, other than that they are forecasts of the future that can be useful for decision-making, then you should read the article.

The main results categories New Zealand's territorial authorities (TAs) by the probability that they will experience a decline in population over the decades 2023-2033 and 2043-2053. I won't spoil the results by naming particular TAs, but here's a summary:
...the number of TAs appearing in each category increases between the two periods. More TAs are facing population decline in the 2043–2053 decade than in the 2023–2033 decade. This corroborates recent work that has shown similar results... In the 2023–2033 decade 20 TAs face a 90 percent or greater probability of population decline, compared with 26 TAs in the 2043–2053 decade. Granted, these TAs have relatively small population, representing 12.2 percent of the national population in 2023 (for the 2023–2033 group based on median population size) and 17.2 percent of the national population in 2043 (for the 2043–2053 group).
Unsurprisingly, rural and peripheral areas face the highest probability of future population decline. Other papers in that issue of Policy Quarterly posit some reasons why we observe population decline in particular areas. My paper is descriptive and future-focused, and doesn't explore the institutional or other non-demographic factors that might explain why some rural areas, rather than others, are projected to experience population decline. That's something for future research.

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