Signal Forecast error in Korea's Basic Plans widens sharply with the projection horizon

Summary

The study calculates the mean absolute percentage error of Basic Plan demand forecasts by projection length. Errors stay near 4.4 to 4.6 percent one and three years ahead but climb to 7.5 percent at five years, 10.8 percent at seven years and 14.1 percent at ten years. Short-range outlooks therefore remain fairly manageable, while cumulative error grows steadily as the horizon extends. The author links this pattern to the difficulty of absorbing shifts in technology, industrial conditions and policy over long periods. It underpins the later argument that a single point forecast is ill-suited to managing long-range uncertainty.