Decision Tree Analysis: Expected Monetary Value for Project Risk Decisions

PMBOK v8 Definition

Decision tree analysis is a diagramming and calculation technique for evaluating the implications of a chain of multiple options in the presence of uncertainty. Decision trees are used to support selection of the best of several alternative courses of action. Alternative paths through the project are shown in the decision tree using branches representing different decisions or events, each of which can have associated costs and related individual project risks (including both threats and opportunities). The end points of branches in the decision tree represent the outcome from following that particular path, which can be negative or positive. The decision tree is evaluated by calculating the expected monetary value of each branch, allowing the optimal path to be selected.

Why It Matters for the Exam

This concept appears frequently in PMI exam questions on quantitative risk analysis and decision-making under uncertainty. You will encounter it in situational questions where you must calculate the best financial choice among multiple project alternatives, and in definition questions testing your understanding of the decision tree components (decision nodes, chance nodes, net path value, and EMV).

Key Points to Remember (for the exam)

• Main Purpose: Support selection of the best of several alternative courses of action under uncertainty
• Core Components: Decision Node (decision to be made), Chance Node (scenario probability), End of Branch (outcome), Net Path Value (payoffs minus costs)
• Calculation Method: Expected Monetary Value (EMV) = Sum of (probability × net path value) for each branch
• Decision Rule: Select the branch with the highest EMV (when all values are positive) or the least negative EMV
• Critical Inputs: Cost of each decision, scenario probability, reward if it occurs
• Common Confusion: EMV is NOT the same as the net path value; EMV is the probability-weighted average of all possible outcomes for a decision branch
• Risk Inclusion: Both threats (negative outcomes) and opportunities (positive outcomes) are represented in the branches

Typical PMI Exam Example

A project manager must decide between upgrading an existing plant (invest $50M) or building a new plant (invest $120M). Strong demand has 60% probability with $200M reward; weak demand has 40% probability with $90M reward. The upgraded plant shows EMV of $46M, while the new plant shows EMV of $36M. The optimal decision is to upgrade, as it has the higher EMV and avoids the worst-case loss of $30M.

PMI Exam Traps

• Trap: Confusing net path value with EMV

  • Reality: Net path value = payoff minus investment cost for ONE specific path; EMV = probability-weighted average of ALL net path values for a decision branch

• Trap: Forgetting to subtract investment costs when calculating net path value

  • Reality: The net path value is computed as "payoffs minus costs" along that specific path

• Trap: Selecting the branch with the highest possible payoff instead of the highest EMV

  • Reality: EMV accounts for probability, so a lower payoff with higher probability may be the better decision

• Trap: Ignoring that threats and opportunities both appear in decision tree branches

  • Reality: Both negative outcomes (threats) and positive outcomes (opportunities) are modeled with their associated probabilities

Important PMI Connections

Quick Review Questions

1. A project manager is evaluating two options: Build New Plant (invest $120M) with 60% chance of $200M revenue and 40% chance of $90M revenue. What is the EMV for the "Build New Plant" decision branch?

2. What is the difference between a "Decision Node" and a "Chance Node" in a decision tree diagram?

3. When calculating net path value, what two elements must be considered for each branch?

4. If one decision branch has a higher possible payoff but lower EMV than another branch, which should be selected according to decision tree analysis?

5. How does the decision tree technique account for both project risks and opportunities in the analysis?

PMBOK v8 Reference

Section 5.3.2.4 - Data Analysis: Decision Tree Analysis