The question of improved data for planning is of great importance. If a country's economic and social services are to be geared to serving the population as a whole, they should be developed in accordance with existing patterns and the possibilities for acting on them. The achievement of high response rates is of great importance in survey research. Confident generalizations can be made about the universe of study only if probability sampling has been adhered to and a high level of response obtained.
Social and demographic statistics are inadequate for many reason. Suppliers of information may falsify reports. People interviewed may answer questions inaccurately because they do not understand the questions or they feel answering may jeopardize them in some way. Different and seemingly comparable sets of information may differ because of differences in the time frame when the information was gathered, what kind of questions were asked, and who asked them. Statistics can and frequently are misinterpreted.
In 1991 it was reported by the UN that in compiling its Demographic Yearbook, 102 out of 205 countries or areas considered that their birth registration was complete, and 95 countries or areas indicated complete death registration. The remaining countries either indicated that they consider their birth or death registration less than 90% complete or provided no information at all. Marriage, divorce and foetal death statistics had different degrees of coverage. These figures are considered an improvement on the situation in 1950 when out of 144 countries, only 52 and 53 countries respectively completed birth and death registration. The quality of vital statistics continues to be considered unsatisfactory and is especially weak with respect to causes of death.
[Developing countries] Most of the countries of Africa, Latin America and Asia suffer from major statistical deficiencies. In the case of demographic statistics, for example, underregistration of births or deaths may be as much as 30 to 50%.
All available sources (1999) stress how difficult it is to quantify the number of Gypsies in the world. The current censuses are not very reliable because of the traditional Gypsy nomadism that in spite of being decreasing, especially in some countries, still lasts. Also, many Roma themselves do not admit to their true ethnic origins for economic and social reasons. With much caution, therefore, it is supposed that there are approximately twelve million Gypsies living outside India around the world. Out of that, the European groups count perhaps 10 million people. Most of them live in Central and Eastern Europe and the Balkans, concretely eight million, while the rest of them, almost two million, live in the European Union. Romania is the country with the largest, three million Gypsy population, which corresponds to the 9.15% of the total population. Comparably, there might be equally many Gypsies living in Slovakia, where they represent the second largest minority group. In 1991, when the Roma of former Czechoslovakia obtained the right to freely proclaim themselves as members of a distinct minority in the census, only 80,627 Roma in Slovakia (1.52% of the citizens of Slovakia) officially declared themselves as such. According to estimates of the urban and communal offices of the state administration from 1989, as many as 253,943 Roma lived in Slovakia, thus constituting 4.8% of the population. Since these statistics did not include Roma who have a standard of living comparable to that of the majority population, Roma political and cultural activists estimate that the number of Roma in Slovakia is even higher, citing a figure of 350,000 to 500,000 in Slovakia today. Large number of Roma lives also in the Czech republic (officially only 0.3%, but reaching about half a million as well), Hungary (officially only 3% but probably many more), Poland, former Soviet Union, former Yugoslavia, Bulgaria and Albania. In southern Spain, Gypsies (Gitanos) used to be the largest minority. Gradually many of them assimilated into the mainstream of Spanish society, but others continue to lead their traditional nomadic way of life. Anyway, among the countries of the European Union, Spain has the largest minority of Gypsies (around 600,000). France with about half of that follows, then Greece, United Kingdom, Italy and Portugal.