Tree Diagrams We can analyze this problem with a tree diagram as well. First, construct the tree diagram: The first branch should show "Condition vs No Condition" and the second set of branches should show "Positive Test vs Negative Test." Label the branches with the appropriate probabilities. Multiply down the branches and describe in symbols what each of those four resulting probabilities represent. Now use this tree diagram to compute the following probabilities: Positive Predictive Value (PPV) - The likelihood of having a condition after getting a positive test: P(Have Condition | Test Positive) = Negative Predictive Value (NPV) - The likelihood of not having the condition after getting a negative test: P(No Condition | Test Negative) =