Schmid Comparative Migration Studies (2020) 8:25 Fig. 1 The National Boundary Regime Typology et al. 2017). IMPIC covers 33 OECD countries from 1980 to 2010 (unfortunately, at this point, no data is available after 2010 and it is too resource-intensive for an individual researcher to update it). To measure Citizenship Regime Inclusiveness (CRI), I have created an original dataset that builds on the most essential elements that can be found in the Migration and Integration Policy Index (MIPEX) strand on Access to Nationality (Huddleston and Niessen 2011). In addition, I have relied on data from Stadlmair (2017), Fitzgerald et al. (2014), de Haas et al. (2015) as well as those provided by the Global Citizenship Observatory (GLOBALCIT).2 Called Citizenship Regime Inclusiveness Index (CITRIX), the dataset therefore does not reinvent but rather reassemble the citizenship wheel. I only provide a short description of CITRIX here, while more details and validity tests can be found in Additional file 1. Attempting to find a balance between high spatio-temporal coverage and sufficient unit homogeneity, the case selection criteria are as follows. For pragmatic reasons, a country must be covered by both IMPIC and CITRIX. In terms of substance, a country must have been an independent and liberal-democratic state, whose adherence to rule of law and whose effective state apparatus mean that policy outputs are implemented. Even though such states do not necessarily have a net migration rate that is tilted towards immigration rather than emigration over the whole period, one can assume that all of them are attractive for migrants as countries of destination. IMPIC and CITRIX overlap for 23 OECD countries from 1980 to 2010 (though CITRIX is also available until 2014). These countries also fulfil the substantive case selection criteria. They include the EU member states forming the EU-15, Norway, Switzerland, Iceland, and Japan, as well as the classical 2 www.globalcit.eu Page 10 of 20