Complete the following steps to specify the column of data that you want to analyze.
You must have at least 2 full seasons of data for Minitab to perform the analysis. However, it is recommended that you have 4 to 5 full seasonal cycles. If you do not have enough full cycles, you many not have enough data to calculate reasonable estimates of the seasonal indices.
If you do not know the seasonal length, use or to help you identify the length.
In this worksheet, Sales contains the number of computers that are sold each month.
C1 |
---|
Sales |
195000 |
213330 |
208005 |
249000 |
237040 |
You should not fit a multiplicative model when your data contain negative values. When you have positive and negative data, the multiplicative seasonal indices for the negative data are the inverse of what they are for the positive data. This causes the model to not fit the data.
Choose the components to include in the model. If you are unsure, use to determine whether your data has a trend.
Complete the following steps to generate forecasts for your time series.
If you enter a value, Minitab uses only the data up to that row number for the forecasts. The forecast values differ from the fits because Minitab uses all of the data to calculate the fits.