Smoothing Migration Intensities with P-TOPALS

Abstract

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 penalised 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.