The DTREE Procedure

The MODIFY statement is used to change either the type of a stage or the reward from an outcome. If MODIFY outcome-name REWARD new-value is given where the outcome-name is an outcome specified in the STAGEIN= data set, and new-value is a numeric value, then the reward of the outcome named outcome-name is changed to new-value.

If MODIFY stage-name TYPE is given where stage-name is a stage name specified in the STAGEIN= data set, then the type of the stage named stage-name is changed to 'DECISION' if its current type is 'CHANCE' and is changed to 'CHANCE' if its current type is 'DECISION'. You cannot change the type of an 'END' stage. The change of the type of a stage from 'CHANCE' to 'DECISION' can help the decision-maker learn how much improvement can be expected if he or she could pick which of the future (or unknown) outcomes would occur. However, if you want to change the type of a stage from 'DECISION' to 'CHANCE', the procedure is not able to determine the probabilities for its outcomes unless you specify them in the PROBIN= data set.