How to Calculate Demographic Indicators of Cities and Municipalities Correctly? A Method to Reassess Official Data for Effects of Municipality Territorial Reforms
The numbers of population, of births and deaths, and of migration as well are important indicators for appraising the demographic development at the local level of cities and municipalities. However, the information of these numbers becomes ambiguous in cases of municipality reforms (e.g. mergers, split-ups) that may cause purely statistical movements of population between municipalities with effects on the numbers of population and related statistics. On the territory of the former GDR, many changes of the territorial map of municipalities (and counties as well) have occurred since the unification in 1990, particularly due to local government reforms. On the other hand, the demography of East Germany has changed remarkably during the last 25 years. This demographic change raises a lot of questions and fears that cannot be managed without taking the demographic development of single locations into account, especially over long periods. The municipal register, provided by the German Federal Statistical Office, contains annual population numbers of each municipality at the end of each period for the respective municipal boundaries. Changes of municipal boundaries are published annually in respective lists of territorial changes. The present paper describes a method of transforming population numbers of cities and municipalities (and also of counties, as well) from municipal boundaries of former periods to municipal boundaries of other, more recent periods. The method is also applicable for other demographic measures, as well as for data that may be supposed to be proportionally related to population.