Combined Method to Upraise Forecasting Accuracy

Formerly, following method was proposed by us. Focusing that the equation of exponential smoothing method was equivalent to (1,1) order ARMA model equation, new method of estimation of smoothing constant in exponential smoothing method was proposed. In this paper, utilizing above stated method, revised forecasting method is proposed. In making forecast such as sales data, seasonal trend is removed by dividing the original time series by Monthly Ratio which is calculated using moving average data. Utilizing above stated method, forecasting is executed with this data in which seasonal trend is removed. Monthly Ratio is multiplied after that, and forecasting data is obtained. This is a revised forecasting method. Variance of forecasting error of this newly proposed method is assumed to be less than those of previously proposed method. These method are examined by the sales data. These results are compared with those of ARIMA model. Some favorable results are obtained.