The Accuracy of Age-specific Population Estimates for Small Areas in Britain

Population estimates play an important role in the allocation of resources at many levels of government and commerce but little is known about the accuracy of age-specific population estimates. Such knowledge is crucial, as resource allocation is often targeted at populations of particular age, and decisions need to be based on the reliability of the estimates. This paper presents a multi-level statistical analysis of the accuracy of age-specific population estimates made for British local authorities in 1991. The aim of this work is to identify the factors that influence accuracy, and to investigate how these influences interact. Our analyses show that the following area characteristics are key factors: true population size; intercensal population change; and percentages of unemployed residents, armed forces residents, and students. In addition, we find that the overall type of method used to calculate estimates is important, and that its effect varies both with area characteristics and with age-group. Local census methods are found to be generally superior, but a low-cost apportionment method, if implemented well, may be as effective.