Assessing the quality of data on international migration flows in Europe: the case of undercounting

Migration Studies, 12:2, 1–21 (2024)
Open Access


Undercounting is a critical issue in migration statistics, resulting in bias. This typically arises from insuf-
ficient reporting requirements and problems with enforcing such requirements. The main sources of
information on undercounting are the metadata accompanying official statistics and expert opinions.
However, metadata and arbitrary expert opinions may be limited by overlooking important details in
migration data shared by various countries. This includes potential oversight of changes in methodolo-
gies, definitions, or retrospective updates to the data following censuses. This work presents a meth-
odological solution with three objectives to address undercounting in international migration data.
First, we provide an overview of available metadata and expert opinions on undercounting in European
migration flows. Secondly, we propose a novel data-driven approach that incorporates year-specific
and duration-of-stay-adjusted classifications. The proposed methodological solution relies on compari-
sons of flows in the same direction reported by a given country with high-quality data reported by
another set of countries. We use bilateral migration data provided by Eurostat, United Nations, and
selected national statistical institutes. Duration-of-stay correction coefficients are derived through an
optimization model or borrowed from the literature. Metadata and expert opinion scores can also be
integrated to classify undercounting. Finally, we provide a dynamic classification of undercounting for
thirty-two European countries (2002–21), accessible through an online Shiny application, offering flexi-
bility and adaptability. The findings highlight significant undercounting in new European Union
Member States, particularly Bulgaria, Latvia, and Romania. Interestingly, other European countries,
including those presumed to maintain reliable population statistics, also exhibit notable periods of

Schlagwörter: Europa
Das Max-Planck-Institut für demografische Forschung (MPIDR) in Rostock ist eines der international führenden Zentren für Bevölkerungswissenschaft. Es gehört zur Max-Planck-Gesellschaft, einer der weltweit renommiertesten Forschungsgemeinschaften.