Volume 43 - Article 55 | Pages 1607–1650
Smoothing migration intensities with P-TOPALS
|Date received:||04 Oct 2019|
|Date published:||15 Dec 2020|
|Keywords:||census data, kernel regression, migration, model migration schedule, penalised splines, P-TOPALS, smoothing|
|Additional files:||readme.43-55 (text file, 789 Byte)|
|demographic-research.43-55 (zip file, 2 MB)|
Background: Age-speciﬁc migration intensities often display irregularities that need to be removed by graduation, but two current methods for doing so, parametric model migration schedules and non-parametric kernel regression, have their limitations.
Objective: This paper introduces P-TOPALS, a relational method for smoothing migration data that combines both parametric and non-parametric approaches.
Methods: I adapt de Beer’s TOPALS framework to migration data and combine it with penalized splines to give a method that frees the user from choosing the optimal number and position of knots and that can be solved using linear techniques. I compare this method to smoothing by model migration schedules and kernel regression using one-year and ﬁve-year migration probabilities calculated from Australian census data.
Results: I ﬁnd that P-TOPALS combines the strengths of both student model migration schedules and kernel regression to allow a good estimation of the high-curvature portion of the curve at young adult ages as well as a sensitive modelling of intensities beyond the labour force peak.
Conclusions: P-TOPALS is a useful framework for incorporating non-parametric elements to improve a model migration schedule ﬁt. It is ﬂexible enough to capture the variety of proﬁles seen for both interstate and regional migration ﬂows and is naturally suited to small populations where observed probabilities can be highly irregular from one age to the next.
Contribution: I demonstrate a new method for migration graduation that brings together the strengths of both parametric and non-parametric approaches to give a good general-purpose smoother. An implementation of the method is available as an Excel add-in.
Sigurd Dyrting - Charles Darwin University, Australia
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