Abstract
Statistics on internal migration are important for keeping estimates of subnational population numbers up-to-date, as well as urban planning, infrastructure development, and impact assessment, among other applications. However, migration flow statistics typically remain constrained by the logistics of infrequent censuses or surveys. The penetration rate of mobile phones is now high across the globe with rapid recent increases in ownership in low-income countries. Analyzing the changing spatiotemporal distribution of mobile phone users through anonymized call detail records (CDRs) offers the possibility to measure migration at multiple temporal and spatial scales. Based on a dataset of 72 billion anonymized CDRs in Namibia from October 2010 to April 2014, we explore how internal migration estimates can be derived and modeled from CDRs at subnational and annual scales, and how precision and accuracy of these estimates compare to census-derived migration statistics. We also demonstrate the use of CDRs to assess how migration patterns change over time, with a finer temporal resolution compared with censuses. Moreover, we show how gravity-type spatial interaction models built using CDRs can accurately capture migration flows. The results highlight that estimates of migration flows made using mobile phone data is a promising avenue for complementing more traditional national migration statistics and obtaining more timely and local data.
Highlights
Human populations are highly mobile in the modern world, and migration is one of the main factors that determines changes in population size, distribution, and structure (Abel and Sander, 2014; Agliari et al 2018)
The Zambezi region lost a significant proportion of its population (5.5%), which was attributed to displacement due to floods in the period of April-June 2010, out of the time frame of the census and call detail records (CDRs) (International Federation of Red Cross and Red Crescent Societies, 2011; Namibia Statistics Agency, 2015)
According to definitions used in census (SI text) (Namibia Statistics Agency, 2015), if people moved to the places of displacement before September 2010 and still lived in the same places by the time of census, they should be considered as non-migrants
Summary
Human populations are highly mobile in the modern world, and migration is one of the main factors that determines changes in population size, distribution, and structure (Abel and Sander, 2014; Agliari et al 2018). Based on a multiannual CDR dataset in Namibia, for the first time, we assess how CDRs as a novel data source might be used efficiently and accurately to replicate the internal migration statistics produced in a census, and examine how CDRs could improve the estimates made using classical gravity models.
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