The aim of this report is to document work done for Task 6.1. The task was to answer the following research question: how well do publicly available statistics on international migration for European countries, more in particular statistics on international migration from national statistical agencies, reflect the true migration flows? They have attempted to answer this question by eliciting expert opinions on measurement accuracy and undercount. During the summer and autumn of 2020, they carried out a two-round Delphi survey among 15 migration experts, preceded by a pilot survey with eight participants. The online questionnaire included questions on measurement accuracy of migration data from population registration systems and from migrant surveys, on possible undercount of immigration and emigration flows, and on the assumed impact of the Covid-19 pan-demic on European migration flows.
This report consists of two parts. Part I, written by Nico Keilman, focuses on elicitation of expert opinions. Part II, of which Georgios Aristotelous is the author, documents how expert opinions on undercount and accuracy were transformed into statistical distributions. The latter distributions form part of the input for the model for estimating true migration flows.