The following actual demand and forecast values are given for the past four periods. We want to calculate MAD, MSE and MAPE for this forecast to see how well it is doing.		The following actual demand and forecast values are given for the past four periods. We want to calculate MAD, MSE and MAPE for this forecast to see how well it is doing.
Note that Abs (et) refers to the absolute value of the error in period t (et).		Note that Abs (et) refers to the absolute value of the error in period t (et).
Period	Actual Demand	Period	Actual Demand	Abs (et)	et2	[Abs (et) / Dt] x 100%
1	56	111	166
2	58	114	170
3	54	105	156
4	65	126	187
Calulation:
MAD
MSE
MAPE