Measuring Hard-to-reach Groups in Administrative Sources

The document aims to support experts working in national statistical offices and other agencies producing official statistics in using data from administrative sources for measuring hard-to-reach groups, namely the homeless, undocumented migrants, immigrants and emigrants. The document also helps data users understand the potential and limitations of administrative sources for producing official statistics on these groups. The document was endorsed by the Conference of European Statisticians at its 2025 plenary session in June 2025.