Evaluating Forecast Error in State Population Projections Using Census 2000 Counts

摘要

In order to determine if a popular summary statistic, the mean absolute percentage error (MAPE), is a valid measure of forecast error for the Census Bureau's 1995 to 2000 state population projections, statistical tests and graphs were used to determine if the error distribution is strongly influenced by outliers. It was found that the absolute percentage error distribution is skewed and asymmetrical. Since the MAPE understates accuracy, MAPE-R, a variant of MAPE derived from the transformed absolute percentage error distribution was accepted as more accurate. Using simple extrapolated projections as a standard to compare forecast error, the findings suggest that the Census Bureau's projections are fairly accurate over a short projection horizon.