The authors evaluate the forecasting accuracy of population projections formulated at state and county levels for Florida. They find that "projections of Florida population made in the 1970s and 1980s had errors...of approximately 2-3 percent for 5-year horizons, 5-6 percent for 10-year horizons and 8-9 percent for 15-year horizons. County projections had errors averaging approximately 5, 10 and 15 percent for these three lengths of horizon, respectively. Based on comparisons with other studies of state and substate population projections, we believe this is a good record of forecast accuracy...."
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