The paper deals with uncertainty in estimating international migration flows for an interlinked system of countries. The related problems are discussed on the example of a dedicated model 'IMEM' (Integrated Model of European Migration). The IMEM is a hierarchical Bayesian model, which allows for combining data from different countries with meta-data on definitions and collection methods, as well as with relevant expert information. The model is applied to 31 EU and EFTA countries for the period 2002-2008. The expert opinion comes from a two-round Delphi survey carried out amongst 11 European experts on issues related to migration statistics. The adopted Bayesian approach allows for a coherent quantification of uncertainty stemming from different sources (data discrepancies, model parameters, and expert judgement). The outcomes produced by the model - whole posterior distributions of estimated flows - can be then used for assessing the true magnitude of flows at the European level, taking into account relative costs of overestimating or underestimating of migration flows. In this context, problems related to application of the decision statistical analysis to multidimensional problems are briefly discussed.

This research is funded by the NORFACE project 'IMEM: Integrated Modelling of European Migration'. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors and should not be attributed in any manner to the institutions, with which they are affiliated.

Keywords: European migration; Migration estimates; Bayesian methods; Uncertainty

Biography: Dr Jakub Bijak is a Lecturer in Demography at the University of Southampton and an Associate Member of the Central European Forum for Migration and Population Research in Warsaw, where he had worked as a researcher until 2008. He holds PhD in economics, with specialisation in demography, obtained from the Warsaw School of Economics. In the period 2001–2003 he worked in the Demographic Unit of the UN International Criminal Tribunal for the former Yugoslavia in The Hague, analysing population consequences of armed conflicts in the Balkans in the 1990s. His research interests focus on the applications of quantitative methods in demography, in particular in migration estimation and forecasting, mortality, and demography of conflict and violence. He is particularly interested in applications of Bayesian methods and in decision-making under uncertainty. He has recently published a book with Springer, entitled Forecasting International Migration in Europe: A Bayesian View.