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Chapter 7—Specialty Packaging Corporation, Part A
The results for this case are obtained using the accompanying spreadsheet Chapter 7—SPC case study
answer. Given the clear seasonal pattern in the data, the forecast is made using the static forecasting
method (with trend and seasonality) and Winter’s model (both outlined in Chapter 7).
Static Forecasting Method
The result for the static forecasting method is contained in the worksheet Static Forecast. For black
plastic, the first step is to obtain deseasonalized demand using Equation 7.2. This is obtained in Cells
D31:D46. The next step is to run a regression between deseasonalized demands and period value
(contained in Cell B31:46). The results of the regression are contained in Cells R28:Z47. The
deseasonalized demand in period 0 is given by the Intercept in Cell S46. The trend is given by the value
in Cell S47. These two values are used to obtain the deseasonalized demand values in Cells E29:E48
based on the regression. The ratio of the actual demand in Cells C29:48 and the deseasonalized demand
in Cells E29:E48 is used to estimate the seasonal factors in Cells F29:F48. The seasonal factors are then
averaged in Cells S53:S56. The average seasonal factors are then used to evaluate the forecasts in Cells
G29:G60 using Equation 7.1. The results are as follows:
The various error estimates are shown in Cells I29:P48.
