Monitor the adjusted exponential smoothing forecast in Problem 12.13 for bias using a tracking signal and a control chart with ±3 MAD. 

Data in Problem 12.13

The Willow River Mining Company mines and ships coal. It has experienced the following demand for coal during the past eight years:

Develop an adjusted exponential smoothing model (α = .30, β = .20) and a linear trend line model, and compare the forecast accuracy of the two using MAD. Indicate which forecast seems to be most accurate.

Year Coat Sales (Tons) 1 4260 2 4510 3 4050 4 5 6 7 8 3720 3900 3470 2890 3100