Surrogates

CRT and QUEST can use surrogates for independent (predictor) variables. For cases in which the value for that variable is missing, other independent variables having high associations with the original variable are used for classification. These alternative predictors are called surrogates. You can specify the maximum number of surrogates to use in the model.

• By default, the maximum number of surrogates is one less than the number of independent variables. In other words, for each independent variable, all other independent variables may be used as surrogates.
• If you don't want the model to use surrogates, specify 0 for the number of surrogates.

To Specify Surrogates

This feature requires the Decision Trees option.

1. From the menus choose:

   Analyze > Classify > Tree...

2. In the main Decision Tree dialog box, for the growing method, select CRT or QUEST.
3. Click Criteria.
4. Click the Surrogates tab.