Population projections are key elements of many planning or policy studies, but are inherently inaccurate. This study of past population projection errors provides a means for constructing confidence intervals for future projections.
We first define a statistic to measure projection errors independently of the size of the population and length of the projection period. A sample of U.S. Census Bureau and U.N. projections indicates that the distribution of the error statistic is relatively stable. Finally, this information is used to construct confidence intervals for the total population of the United States through the year 2000
