The Estimation of Seasonal Variation in Economic Time Series

The problem of estimating the seasonal component in an economic time series is discussed and it is pointed out that the effects of any moving average operator on the seasonal component may be easily reversed so that one may use any suitable operator to remove the trend. The computational procedure is to estimate the seasonal index for the trend free series and to convert this index into a seasonal index for the original series by taking 12 term moving averages of this series (continued periodically) with weights depending on the operator used to remove trend. Weights for some commonly used operators are tabulated. The problem of estimating a slowly evolving seasonal is considered.