(a) In exponential smoothing we use two terms: At and Ft
At is used for Actual Demand
Ft is used for Forecasted Demand
The formula used is Ft+1 = αAt + (1-α)Ft
Substituting α= 0.2 (mentioned in the question)
Ft+1 = 0.2At + 0.8Ft
To calculate F2 we need values of A1 and F1. We have value of A1 but not F1. So we can assume A1 = F1 for calculating values further
Month |
Demand |
1 |
11 |
2 |
14 |
3 |
15 |
4 |
14 |
5 |
15 |
6 |
19 |
F2 = 0.2*A1 + 0.8*F1
F2 = 0.2*11 + 0.8 * 11
=11
F1 and F2 values are same. So, we can safely assume A1 = F2 and calculate further based on this assumption
When calculated using the above mentioned formula, forecasted values are as mentioned below
Month |
Demand |
Forecast |
1 |
11 |
|
2 |
14 |
11 |
3 |
15 |
11.6 |
4 |
14 |
12.28 |
5 |
15 |
12.624 |
6 |
19 |
13.0992 |
MAD is Mean Absolute Deviation.
Deviation = Actual value – Forecast value
For ex, for month 4 , Deviation = 14 – 12.28 = 1.72
Absolute deviation means absolute value of the deviations calculated
Month |
Demand |
Forecast |
Deviation |
Absolute deviation |
1 |
11 |
|
|
|
2 |
14 |
11 |
|
|
3 |
15 |
11.6 |
3.4 |
3.4 |
4 |
14 |
12.28 |
1.72 |
1.72 |
5 |
15 |
12.624 |
2.376 |
2.376 |
6 |
19 |
13.0992 |
5.9008 |
5.9008 |
MAD is the average of absolute deviations
Since, F2 is based on the assumption, we consider deviations from month 3 for calculating MAD.
MAD = ( 3.4+1.72+2.376+5.9008)/4 = 3.3492
(b) In moving average, demand for current month is forecasted as an average of previous months. So, in a 3 month moving forecast, the fourth month forecast would be the average of demand of first three months. Also, we start forecasting from fourth month because until third month we donot have values to calculate a 3 month moving average.
Once we have forecasted values, MAD is calculated in similar way as mentioned in part (a).
The following table is the result
Month |
Demand |
Forecast |
Deviation |
Absolute Deviation |
1 |
11 |
|
|
|
2 |
14 |
|
|
|
3 |
15 |
|
|
|
4 |
14 |
13.3333 |
0.6667 |
0.6667 |
5 |
15 |
14.3333 |
0.6667 |
0.6667 |
6 |
19 |
14.6667 |
4.3333 |
4.3333 |
MAD =(0.6667+0.6667+4.3333)/3 =1.8889
(c) MSE is the mean square error . It is the average of squares of the errors or deviations.
MSE =( 0.66672 + 0.66672 + 4.33332 )/3 = 6.5556
(d) II since MAD is less