Measuring Internal Migration: Comparing Census and Administrative Data
Foley, B., Champion, T. & Shuttleworth, I. (2017) UK Administrative Data Research Network Annual Research Conference, Royal College of Surgeons, Edinburgh, UK, 1 - 2 June 2017 [NILS]
Internal migration, the movement of people within a country, is a key component of sub-national population re-distribution. However, unlike births and deaths which are measured accurately via registration systems, internal migration is difficult to quantify. Typically, data are collected in many countries through censuses or by the use of administrative sources with a move being defined either as a transition between places over one year, five years, or between censuses, or else as an individual event occurring over a defined time period. Each of these approaches has its strengths and weaknesses. Censuses provide high population coverage but, as in the UK, knowledge of moves is restricted to what happened in the preceding year. Administrative data collect information on the multiple moves that might occur over a time period, which are missed in a census. However, administrative systems rely on being updated regularly and sometimes individuals are slow in doing so. Each approach therefore captures imperfect information on a population in flux.
In this presentation, we therefore investigate internal migration in Northern Ireland (NI) using data from the 2011 NI Census and the health card registration system (HCRS), held in the Northern Ireland Longitudinal Study (NILS), a 28% representative sample of the population. We consider residential moves between Super Output Areas (SOAs) that are observed in the Census and not the HCRS (and vice versa) over various time periods, we assess the geographical comparability of flows between places using both sources, and we estimated models of the propensity to move using census and health record data. Our aim is to inform debates about the measurement of internal migration using administrative sources, a relevant topic given the increasing use of these data by national statistical institutes in the UK and elsewhere to support the production of population statistics.