Hi all,
Dr. Marseille also reviewed your first assignment on mammography decision trees and thought they were excellent! If he had any additional comments for you, I e-mailed them to you.
He wanted to pass along some rules of thumb for decision trees:
- The decision node at the beginning does not have associated probabilities - participants are "randomized" to the decision strategies. No decisions after the initial decision node. It is followed by chance nodes and terminal nodes.
- Probabilities stemming from chance nodes must add to 100%. In Excel, create a formula =1 - cell to accomplish this. In TreeAge, use # symbols.
- All chance nodes need to have probabilities assigned to them.
- All terminal nodes need to have utilities assigned to them.
- Probably better to treat the screening arm as “annual screening over X years” rather than portraying the results as successive screenings. Explicitly portraying of successive screenings is good, but may be overly-cumbersome for our purposes in this class. In the Markov modeling lecture, we will cover how to do repeated cycles.
Note: I also was mistaken in several of my comments to you - The prevalence of cancer in screening group and no-screening group are the same. The true disease prevalence is the same, although screening may detect more.
Feel free to e-mail with any questions!
Best,
Sri Lekha Tummalapalli