Estimating internal migration between Northern Territory SA3 regions

Projecting migration between small areas such as SA3s in the Northern Territory, and other areas withrelatively small populations, is difficult given the small number of migration ‘events’ on which toestimate probabilities. The aim of this paper is to explore the feasibility of estimating internal migrationprobabilities for a multi-regional population projection model at 1-year age and time intervals. To doso, we examine the feasibility of applying a polynomial smoothing technique called PTOPALS toestimate migration probabilities between the Northern Territory’s nine SA3 regions at one-yearintervals by age, Indigenous status, and sex.We find that it is feasible to calculate demographically plausible estimates for internal migrationbetween NT SA3 regions. Much of the process can be automated in R scripts, but some steps are manual(extraction of data from TableBuilder, review of the calibration reports) and subjective (assessments ofplausibility and adjustment of method parameters).With minor modifications the method we use here could be adapted to SA3-specific interstatemigration. It could also be adapted to estimate inter-SA2 migration, but migration ratios at the SA2level will likely display very high levels of noise. To overcome this, it might be possible to get reasonableestimates by pooling data from multiple Censuses. Otherwise, the SA3-level estimates given here couldbe used to assign reasonable values to SA2-level ratios with some additional assumptions.