Another is that expert sources often report absolute numbers without giving a year of reference. For example an otherwise-useful global reference, Ethnic Groups Worldwide, reports numbers of group members without any years of reference or sources. Most of the more detailed studies prepared by the Minority Rights Group, many of them summarized in the World Directory of Minorities , provide more demographic details. We gave precedence to sources that compiled estimates for a particular type of group or region, on the assumption that the authors imposed some quality control on estimates, or at least were consistent in the types of information used. In a relatively small number of instances we relied on assessments by group or country experts.
State formation has a major impact on group population percentages.
We used these republican census results to obtain percentages that we then applied to 1990s population estimates for the newly independent states, all of which inherited Communist-era boundaries. Population movements , especially refugee flows, lead to changes over time in group population percentages, such that a proportion based on information from the 1980s sometimes cannot be reliably applied to country population in the 1990s. This especially affects estimates of minority populations in the Soviet and Yugoslav successor states as well as estimates of communal group size in the Greater Horn of Africa. A Comparative Handbook , usually do not or cannot take account of such movements. We have used refugee data and expert estimates, where possible, to adjust data derived from these sources.