The VPC statement causes PROC TREE to compute the value of perfect control (the value of controlling an uncertainty). The effect of perfect control is that you can pick the outcome of an uncertain stage. This value gives an upper limit on the amount you should be willing to spend on any control procedure. Only the name of a chance stage can be used to calculate the value of perfect control. The procedure evaluates the decision tree, if it has not already done so, before computing this value.