The last four weekly values of sales were 80, 100, 105, and 90 units, respectively. The last four forecasts (for the same four weeks) were 60, 80, 95, and 75 units, respectively. Calculate the MAD, MSE, and MAPE for these four weeks

Sales Forecast Error Error squared Pct. error
80 60 20 400 .25
100 80 20 400 .20
105 95 10 100 .095
90 75 15 225 .167

MAD = 65/4 = 16.25; MSE = 1125/4 = 281.25; MAPE = 0.712/4 = .178 or 17.8%