FORCE Keyword (TREE command)

• By default, the procedure evaluates each predictor variable for inclusion in the model. The optional FORCE keyword forces an independent variable into the model as the first split variable (the first variable used to split the root node into child nodes).
• The FORCE keyword must be followed by an equals sign (=) and a single variable.
• A measurement level may be specified in square brackets following the variable name. If the variable is also included in the independent variable list, the measurement level specified for the FORCE variable is used. If the variable has a specified measurement level in the independent list but no explicit measurement level on the FORCE specification, the defined measurement level for the variable is used.
• The variable cannot be the dependent variable or the WEIGHT variable.

Example

TREE risk [o] BY income [o] age [s] creditscore [s] FORCE = gender [n].

• The independent variables income, age, and creditscore may or may not be included in the model, depending on how strongly they interact with the dependent variable risk.
• The independent variable gender will be included in the model regardless of the level of interaction with the dependent variable, and the root node will first be split into nodes for male and female before any other independent variables are considered.