The MIPEX (Migrant Integration Policy Index) is a relatively widely used index. I have demonstrated empirically that it can be used as a scale, but have voiced some concerns about the weak theoretical foundation.
The number of countries covered by the MIPEX is increasing, and there are 148 indicators available. In an attempt to make most of these data, I have picked the parts of the MIPEX that most closely fit the typology developed in Koopmans et al. (2005).
We can discuss the labels, but there are clear differences between countries, and citizenship regimes are clearly dynamic. This means that, yes, citizenship regimes are worth investigating, but country dummies will fail to provide an accurate picture.
Koopmans, Ruud, Paul Statham, Marco Giugni, and Florence Passy. 2005. Contested Citizenship: Immigration and Cultural Diversity in Europe. Minneapolis: Minnesota University Press.
Ruedin, Didier. 2011. “The reliability of MIPEX indicators as scales.” SOM Working Paper 3: 1–19.