MANGT 515 Prospective Students

Trend-Adjusted Exponential Smoothing

The exponential smoothing approach discussed above is an appropriate forecasting technique, if the time series exhibits a horizontal pattern (i.e. No trend) with random fluctuations. However, if the time-series exhibits trend, forecasts based on simple exponential smoothing will lag the trend. In such cases, a variation of simple exponential smoothing called the trend-adjusted Exponential smoothing can be used as a forecasting technique. "The trend-adjusted forecast (TAF) has two components:

  1. A smoothed error
  2. A trend factor
  3. TAFt = St-1 + Tt-1 , where

    St-1 = Previous period smoothed forecast

    Tt-1 = Previous period trend estimate

    TAFt = Current period's trend-adjusted forecast

    St = TAFt + alpha(At - TAFt)

    Tt = Tt-1 + beta(TAFt - TAFt-1 - Tt-1), where alpha and betaare smoothing constants

In order to use this method, one must select values of alpha and beta (usually through trial and error) and make a starting forecast and an estimate of the trend" (Stevenson, 2005).