Introduction to TreeAgeIntroduction to TreeAge

June 1, 2005June 1, 2005Mendel E. Singer, Ph.D.Mendel E. Singer, Ph.D.Case School of MedicineCase School of Medicine

mendel@case.edumendel@case.edu

Assumptions Assumptions (always dangerous)(always dangerous)

You’re already familiar with the essential You’re already familiar with the essential components of a decision analysiscomponents of a decision analysis

You’ve been introduced to the basic idea You’ve been introduced to the basic idea of cost-effectiveness analysisof cost-effectiveness analysis

You may not be comfortable with a You may not be comfortable with a decision tree, but you’ve seen a fewdecision tree, but you’ve seen a few

You haven’t programmed any decision You haven’t programmed any decision trees, or did once upon a time, but……trees, or did once upon a time, but……

What’s TreeAge?What’s TreeAge?

TreeAge (pronounced “triage”) is software TreeAge (pronounced “triage”) is software specifically for doing decision analyses, and specifically for doing decision analyses, and cost-effectiveness analyses that are based on cost-effectiveness analyses that are based on the decision analytic model.the decision analytic model.Until recently it was called DATA, but the Until recently it was called DATA, but the company’s catchy name, TreeAge, is what company’s catchy name, TreeAge, is what stuck, and everyone called it that anyway.stuck, and everyone called it that anyway.Originally developed for business applications, Originally developed for business applications, they have been developing for health care they have been developing for health care applications for close to 10 years now.applications for close to 10 years now.

Why Use TreeAge?Why Use TreeAge?

Some people use TreeAge, others use Some people use TreeAge, others use alternative decision analysis software like alternative decision analysis software like DecisionMaker, some use Excel, and some use DecisionMaker, some use Excel, and some use computer simulation software.computer simulation software.TreeAge is a mature software product that is TreeAge is a mature software product that is well supported. It is regularly updated and well supported. It is regularly updated and improved, doing a good job of keeping up with improved, doing a good job of keeping up with advancements in the methods.advancements in the methods.It is very intuitive to use because it is based It is very intuitive to use because it is based around the decision tree graphic, and not around the decision tree graphic, and not programming code.programming code.

What Can TreeAge do?What Can TreeAge do?

Decision AnalysisDecision Analysis

Cost-Effectiveness AnalysisCost-Effectiveness Analysis

Baseline and Sensitivity AnalysesBaseline and Sensitivity Analyses

Markov ModelsMarkov Models

Monte Carlo SimulationMonte Carlo Simulation

Influence DiagramsInfluence DiagramsNote: It’s OK not to fully appreciate what all of the Note: It’s OK not to fully appreciate what all of the

above are! You can still follow this lecture!above are! You can still follow this lecture!

Getting the SoftwareGetting the Software

Purchase it!Purchase it!

Perhaps your group already has a site Perhaps your group already has a site licenselicense

Download a trial copy from: Download a trial copy from: www.treeage.comwww.treeage.com– Limited in sizeLimited in size– Works for 21 days from first time it is openedWorks for 21 days from first time it is opened

WARNING!!WARNING!!

You won’t learn to program by watching a You won’t learn to program by watching a lecture. You have to get hands on!lecture. You have to get hands on!

It can help to do some small programs for It can help to do some small programs for practice. I will see if HERC can put this on practice. I will see if HERC can put this on the web site along with this presentation.the web site along with this presentation.

Abdominal Aortic Aneurysm (AAA)Abdominal Aortic Aneurysm (AAA)

We need a simple, and therefore simplified problem to We need a simple, and therefore simplified problem to use as an example.use as an example.AAAs: 5% - 7% of people over age 60AAAs: 5% - 7% of people over age 60Most commonly affect Men, Age 40-70.Most commonly affect Men, Age 40-70.Usually asymptomatic, often until ruptureUsually asymptomatic, often until ruptureOptions are surgery and watchful waiting, with some Options are surgery and watchful waiting, with some decision rule as to when to operate based on the size of decision rule as to when to operate based on the size of the AAA.the AAA.Debate as to how large the aneurysm should be to Debate as to how large the aneurysm should be to recommend surgery.recommend surgery.Our example will be based largely on the work of Katz Our example will be based largely on the work of Katz and Cronenwett (1994).and Cronenwett (1994).

Problem DefinitionProblem Definition

Reference CaseReference Case– 60-year old male60-year old male– 4 cm abdominal aortic aneurysm4 cm abdominal aortic aneurysm– Otherwise, patient is in good healthOtherwise, patient is in good health

Surgery vs Watchful WaitingSurgery vs Watchful WaitingTime horizon: 1 yearTime horizon: 1 yearOutcome Measure: SurvivalOutcome Measure: Survival– Alive = 1Alive = 1– Dead = 0Dead = 0

More Details of the ExampleMore Details of the Example

Simplifications and assumptions:Simplifications and assumptions:– If expansion occurs, it reaches 5.5 cm.If expansion occurs, it reaches 5.5 cm.– Either the AAA ruptures, or surgery is Either the AAA ruptures, or surgery is

performed.performed.– If the AAA ruptures, the patient may die If the AAA ruptures, the patient may die

before emergency surgery can be performed.before emergency surgery can be performed.– No death from other causes during the 1 year No death from other causes during the 1 year

time horizon used for the analysistime horizon used for the analysis

Types of NodesTypes of Nodes

Start with a choice node, with each possible Start with a choice node, with each possible strategy coming out of this node.strategy coming out of this node.Three kinds of basic node types:Three kinds of basic node types:– Choice, or Decision NodeChoice, or Decision Node– Chance NodeChance Node– Terminal NodeTerminal Node

Choice or Decision Chance Terminal

1. Always start with a choice, or decision node

2. Names of nodes go above the branch

3. Note in the properties box that the name is cut off. We can select the vertical bar to the right of the properties box and drag it, to make the box wider.

To add branches there are several techniques.

1. Double-click on the node

2. Right-click on the node and select the choice to add branches.

3. Use the menus to select “Options / Add Branches”

4. Enter Control-A.

By double-clicking on the decision node you get…..

Parameter Values Parameter Values

NameName ValueValue LowLow HighHigh

pDieBeforeSurgerypDieBeforeSurgery 0.550.55 0.270.27 0.820.82

pDieDuringSurgeryAfterRupturepDieDuringSurgeryAfterRupture 0.540.54 0.270.27 0.810.81

pDieElectiveSurgerypDieElectiveSurgery 0.0460.046 0.0230.023 0.0690.069

pDieSurgeryNoRupturepDieSurgeryNoRupture 0.230.23 0.110.11 0.340.34

pExpansionpExpansion 0.0330.033 0.0160.016 0.0490.049

pRupturepRupture 0.920.92 0.880.88 0.960.96

1. Probabilities go below the branch

2. Don’t put in the actual numbers for the probabilities.

3. Instead, use variables. This makes it easy to change its value, even if it appears in many places in the tree. More importantly, it allows us to do sensitivity analysis on that parameter.

Naming VariablesNaming Variables

Use descriptive names. Better to write out long variables, Use descriptive names. Better to write out long variables, than to use abbreviations you may not be sure of when than to use abbreviations you may not be sure of when you open the model many months later to revise it.you open the model many months later to revise it.Use a consistent naming convention. Use a consistent naming convention. Many people begin the name of probability variables a “p”, utilities with a “u”, costs with a “c”, etc….– e.g. mortality rate = pDie– E.g. utility of diabetes = uDiabetes

Make the names easy to read. When using multiple words in a variable name, capitalize the first letter of each new word.– e.g. pDieBeforeSurgery

Some use the underscore character between words.– e.g. pDie_before_surgery

The # SignThe # Sign

In TreeAge, the # sign can be used for a probability.In TreeAge, the # sign can be used for a probability.It indicates the leftover probability, after accounting for It indicates the leftover probability, after accounting for the other branches emanating from the same node.the other branches emanating from the same node.You should use this whenever possible.You should use this whenever possible.Aids sensitivity analysis. When a probability changes Aids sensitivity analysis. When a probability changes value, the sum of the probabilities for the nodes leaving value, the sum of the probabilities for the nodes leaving that chance node will no longer be 1. that chance node will no longer be 1. Try to never use more than 2 branches out of 1 chance Try to never use more than 2 branches out of 1 chance node. This way, whenever one probability changes, we node. This way, whenever one probability changes, we know the other possibility must change by the same know the other possibility must change by the same amount in the opposite direction. E.g. if the baseline amount in the opposite direction. E.g. if the baseline estimate of operative mortality is 0.05, then if that value estimate of operative mortality is 0.05, then if that value were to increase to 0.10, then the probability of surviving were to increase to 0.10, then the probability of surviving the surgery must decrease by the same 0.05 (0.10-0.05).the surgery must decrease by the same 0.05 (0.10-0.05).

1. At each node there is a number in a box indicating the expected value of the outcome from that point forward

2. At the choice node, it also indicates which strategy is optimal. The nodes in the optimal path are all highlighted.

3. At all terminal nodes, it first shows the outcome score associated with that result, and then shows the probability of the path ending in that terminal node.

4. All of the variable names are temporarily replaced by their values.

1. Graph shows how the expected value (mean) changes based on the mortality rate from elective surgery over the range of values specified.

2. Watchful waiting is unaffected because elective surgery isn’t in its path.

3. The point of intersection, known as the threshold value, is shown on the graph and the point and its associated mean is shown in the right margin.