Introduction

In recent years a big demand has developed for estimates of future populations. The main reason for this demand is probably economic: plans for the production of food, the supply of power and the manufacture of goods all need to be based on advance knowledge of likely changes in the numbers of people for whom the production is designed. For instance, demand in the perambulator and baby-carriage trade depends on the number of future births and also on whether they are first births in the family or later children (who may ‘inherit’ such appliances from their elder brothers and sisters). National and local government administration also calls for an appreciation of the outcome of population trends. Demographic changes may affect the relative military strengths of neighbouring countries, the demand for housing and other amenities, and the need for public transport. There is an obvious connection between the size of the future population at the appropriate ages and plans for the construction of schools, the training of teachers, the recruitment of labour and the provision of health services. Calculations of future population for periods varying from one to thirty years, or sometimes even further ahead, are a feature of social security planning: short-term assessments are required for budgetary purposes, and projections of longer range are wanted in order to illustrate the broader financial trends.

An example of a requirement of more limited scope is the assessment of the size and distribution of the population at various points of time between censuses; this is needed as a base for the calculation of birth rates and death rates in the local administrative areas each year and for the country as a whole.