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16.7. Calculation Algorithm for Decision Trees

Applies to: PrecisionTree 5.x–7.x

How does PrecisionTree calculate the values and probabilities it shows next to each node? Why are some nodes marked TRUE and others FALSE?

Short answer:

The value of an end node is the sum of the value of each branch in the path from the root. The percentage (likelihood) of an end node is the product of each branch in the path from the root, counting TRUE as 1 and FALSE as 0.
Working from right to left, the value of a chance node is the weighted average of the values of the nodes that that chance node branches to, and the value of a decision node is the value of the node on the TRUE branch of that decision node.

There's a much more thorough explanation in the PrecisionTree user manual. Click Help » Documentation » Manual and look at Appendix A.

For convenience, those two pages are attached to this article. The information is valid for PrecisionTree up through 7.6. If you have a later release of PrecisionTree, please look at the manual that is installed with your software.

Last edited: 2018-11-30

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