The following times series shows the demand for a particular product over the past 10 months.
Month |
Value |
1 |
324 |
2 |
311 |
3 |
303 |
4 |
314 |
5 |
323 |
6 |
313 |
7 |
302 |
8 |
315 |
9 |
312 |
10 |
326 |
a. Use α = 0.2 to compute the exponential smoothing values for the time series. Compute MSE, MAPE and a forecast for month 11.
b. Calculate MSE and MAPE for three month moving average ?
c. Compare the three-month moving average forecast with the exponential smoothing forecast using α = 0.2. Which appears to provide the better forecast based on MSE?
a. Use α = 0.2 to compute the exponential smoothing values for the time series. Compute MSE, MAPE and a forecast for month 11.
For exponential smoothing we will assume the first month forecast value is same as actual.
For next forecast values we hhvae the formula
Eg: For month 4 we have F4 = A3 * 0.2 + F3*0.8
Month | Value | Forecast |
1 | 324 | 324 |
2 | 311 | 324.000 |
3 | 303 | 321.400 |
4 | 314 | 317.720 |
5 | 323 | 316.976 |
6 | 313 | 318.181 |
7 | 302 | 317.145 |
8 | 315 | 314.116 |
9 | 312 | 314.293 |
10 | 326 | 313.834 |
11 | 316.267 |
MSE = mean squared error
where the error = actual - forecast
So we square the error.
MSE = ......We divide 9 because we have 9 pirs of the actual and forecast.
Month | Value | Forecast | Error | Error^2 |
1 | 324 | 324 | ||
2 | 311 | 324.000 | -13.000 | 169.000 |
3 | 303 | 321.400 | -18.400 | 338.560 |
4 | 314 | 317.720 | -3.720 | 13.838 |
5 | 323 | 316.976 | 6.024 | 36.289 |
6 | 313 | 318.181 | -5.181 | 26.841 |
7 | 302 | 317.145 | -15.145 | 229.360 |
8 | 315 | 314.116 | 0.884 | 0.782 |
9 | 312 | 314.293 | -2.293 | 5.256 |
10 | 326 | 313.834 | 12.166 | 148.010 |
11 | 316.267 | |||
Total | 967.936 | |||
Mean | 107.548 |
MAPE = mean absolute percentage error
Where percentage error = Absolute error / actual
MAPE =
Month | Value | Forecast | Error | Abs error | APE |
1 | 324 | 324 | |||
2 | 311 | 324.000 | -13.000 | 13 | 4.2% |
3 | 303 | 321.400 | -18.400 | 18.4 | 6.1% |
4 | 314 | 317.720 | -3.720 | 3.72 | 1.2% |
5 | 323 | 316.976 | 6.024 | 6.024 | 1.9% |
6 | 313 | 318.181 | -5.181 | 5.181 | 1.7% |
7 | 302 | 317.145 | -15.145 | 15.145 | 5.0% |
8 | 315 | 314.116 | 0.884 | 0.884 | 0.3% |
9 | 312 | 314.293 | -2.293 | 2.293 | 0.7% |
10 | 326 | 313.834 | 12.166 | 12.166 | 3.7% |
11 | 316.267 | ||||
Total | 24.7% | ||||
Mean | 2.7% |
b. Calculate MSE and MAPE for three month moving average ?
Moving average is where we first take the total of previous 'n' periods and then divide by 'n'.
So Eg: we have F4 = (sum (A1 + A2+ A3)/ 3