Evaluation of a simple decision tree

The expected value of any node is simply the probability-weighted average of the outcomes across all of the branches of the node. This is calculated by taking the sum of each branch's value times its probability. For Choice 1 above, the average life expectancy of a cohort of patients undergoing that therapy would consist of the combination of 45 percent who lived 10 years and 55 percent who lived 12 years, for an average of 11.1 years.