Spreadsheet Implementation On Calculate Seasonal Adjustment and Exponential Smoothing

Do a forecasting through multiplicative seasonal adjustment and linear exponential smoothing of

Ý_(t) = 2Y_(t-1) - Y_(t-2) - 2(1- a)e_(t-1) + ((1- a)²)e_(t-2)

Steps :

• First the data must be adjusted seasonally;

• Do a forecast through seasonally data via linear exponential smoothing;

• "reseasonalize" the seasonally adjusted forecasts to have output of forecasts from original series.

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Picture Ilustration Of Input & Output

Here are The Step On Spreadsheet

Seasonal adjustment: on the first 6 column

Linear exponential smoothing

calculate a ( smoothing constant)

For easy, make a range name with Alpha using command: Insert/Name/Create

Others

Significant Degree: 1 - a

Mean square error: MSE= VAR (errors)+ (AVG(errors))².

Confident interval: Ci : Forecast ± RMSE

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