Introduction

Is population forecasting different from other kinds of forecasting, that it should warrant its own special methods and its own special discussion? In some important respects it is; in particular, long-term demographic forecasts many decades into the future may contain more useful information than is true for other forecasts, such as turning points. There are several reasons:

1. The initial age distribution of the population provides early information about future population size, age distribution, and growth rates. For example, since their birth, we have known exactly when the baby boom generations would swell the numbers of elderly.

2. The relative slowness, smoothness, and regularity of change in fertility and mortality facilitate long-term forecasts. Compared to real productivity growth or to real interest rates, for example, the vital rates are less volatile.

3. Fertility, mortality, and nuptiality have highly distinctive age patterns, which have persisted over the several centuries for which they have been observed. These regular and distinctive age patterns make the consequences of initial age distributional irregularities more predictable.

Demographers have developed methods and models for exploiting these features of population evolution in their projections. This does not mean, of course, that demographers have built a sterling record of success in long-term forecasting. Their record, which we will review later, has been a mixture of success and failure.

Demographic forecasts have many uses. A few users, such as the manufacturers of infant formula, are interested in the numbers of births by quarter in the coming year.