The data on enthic fragmentation are based on three sources: Handbook of the Nations (various years), Britannica Book of the Year (various years) and Demographic Yearbook (various years). In some cases the differences between these three sources were tremendous. Handbook of the Nations was very good concerning detailed information about ethnic groups, but lacked information about linguistic groups for most of the countries. It was also difficult to get this kind of information further back than 1979. Britannica Book of the Year turned out to be very good on both linguistic, religious and ethnic groups. However, here it was difficult getting any information further back than 1969. Thus, for information about fragmentation (linguistic, religious or ethnic) for the earlier years, the data are based on Demographic Yearbook, although the given information at some points was not particularly detailed. This was, for instance, especially true for the years 1945-50, where Demographic Yearbook in some cases (countries) categorized all black people as being one single ethnic group called 'Blacks'.
Each source was coded separately. Since none of the sources covered the total range of years, this naturally meant a relatively large number of missing cases. To avoid this, the data was interpolated for the years that were missing. Some numbers and (less likely) names may therefore not be truly correct. However, since these variables are considered to be rather constant over time, this should not be too much of a problem.