Operations and Supply Chain Management The Core

FORECASTING chapter 3 85
18. A particular forecasting model was used to forecast a six-month period. Here are
the forecasts and actual demands that resulted:
April
May
June
July
August
September
FORECAST
250
325
400
350
375
450
ACTUAL
200
250
325
300
325
400
Find the tracking signal and state whether you think the model being used is
giving acceptable answers.
19. Harlen Industries has a simple forecasting model: Take the actual demand for
the same month last year and divide that by the number of fractional weeks
in that month. This gives the average weekly demand for that month. This
weekly average is used as the weekly forecast for the same month this year. This
technique was used to forecast eight weeks for this year, which are shown below
along with the actual demand that occurred.
The following eight weeks show the forecast (based on last year) and the
demand that actually occurred:
WEEK
FORECAST
DEMAND
ACTUAL
DEMAND
WEEK
FORECAST
DEMAND
ACTUAL
DEMAND
1
2
3
4
140
140
140
140
137
133
150
160
5
6
7
8
140
150
150
150
180
170
185
205
a. Compute the MAD of forecast errors.
b. Using the RSFE, compute the tracking signal.
c. Based on your answers to parts (a) and (b), comment on Harlen’s method of
forecasting.
20. In this problem, you are to test the validity of your forecasting model. Here
are the forecasts for a model you have been using and the actual demands that
occurred:
WEEK FORECAST ACTUAL
1
2
3
4
5
6
800
850
950
950
1,000
975
900
1,000
1,050
900
900
1,100
Use the method stated in the text to compute MAD and tracking signal. Then
decide whether the forecasting model you have been using is giving reasonable
results.