Defining a Model

Because the model is dependent upon the design file, the model file must be updated each time the design file is updated. You may have as many different models as you would like for any design; by default, you will get the same number of regression output sets.

Model Type Combobox

The first item on the screen is the Model Type Combobox from which you can select the type of model that will be used in the regression analysis. Remember that you can suppress terms, so pick a model type that has all of the terms that you need and suppress the terms that you don’t want.

b0 CheckBox

STRATEGY for Windows will compute a b0 for you.

If you would not like STRATEGY for Windows to compute a b0, make sure the Compute b0 Checkbox is unchecked. Selecting this option says that you want to force the model through the origin of the X factor system. You may want to do this sometimes, but it is very unusual.

Order TextBox

If you selected Main Effects + Interactions as the model type, you will see an additional question appears at the bottom of the screen. This allows you to specify the highest order of the interaction to appear in the model.

The column names are retrieved from your X,Y List (DES file) and displayed in the three list boxes on this screen. If this is a model file that you have worked on before, your previous choices will be highlighted. Note that RUNORD can be a factor.

Select column names from this list for either Responses, Factors, or Blocking Factors. Each factor selected as a blocking factor must also be selected as a factor (STRATEGY for Windows does this for you automatically if you have not already specified the maximum number of factors.

When the design will permit all of the terms in the model to be fitted to the data, we suggest that you keep all of the terms in the model in order to get the most information from your data. However, you must suppress terms from the model if you know that certain b coefficients cannot be estimated by the design. If you are working with discrete factors, it doesn’t make sense to include terms beyond the interactions for those factors.

Click the Suppress Terms tab to suppress any terms from the model.

Completing the model file is usually done just before a regression is run. If you elect to build the model at this time, you be given the opportunity to proceed directly to the Regression form without returning to the Main Menu.