The grey forecasting model has been successfully applied to finance, physic
al control, engineering, economics, etc. However, no seasonal time series f
orecast has been tested. The authors of this paper proved that GM(1,1) grey
forecasting model is insufficient for forecasting time series with seasona
lity. This paper proposes a hybrid method that combines the GM(1,1) grey fo
recasting model and the ratio-to-moving-average deseasonalization method to
forecast time series with seasonality characteristics. Three criteria, i.e
., the mean squares error (MSE), the mean absolute error (MAE), and mean ab
solute percentage error (MAPE) were used to compare the performance of the
hybrid model against other four models, i.e., the seasonal time series ARIM
A model (SARIMA), the neural network back-propagation model combined with g
rey relation, the GM(1,1) grey model with raw data, the GM(1,N) grey model
combined with grey relation. The time series data of the total production v
alue of Taiwan's machinery industry (January 1994 to December 1997) and the
sales volume of soft drink reported from Montgomery's book were used as te
st data sets. Except for the out-of-sample error of the Taiwan machinery pr
oduction value time series, the MSE, the MAE, and the MAPE of the hybrid mo
del were the lowest. (C) 2001 Elsevier Science Inc.