Probability and Impact Matrix With Scoring Scheme

PMBOK v8 Definition

The probability and impact matrix is a grid for mapping the probability of occurrence of each risk and its impact on project objectives if that risk occurs. It uses numeric values or descriptive terms (such as very high, high, medium, low, and very low) for probability and impact, and where numeric values are used, these can be multiplied to give a probability–impact score for each risk, which allows the relative priority of individual risks to be evaluated within each priority level. Opportunities and threats are represented in a common probability and impact matrix using positive definitions of impact for opportunities and negative impact definitions for threats.

Why It Matters for the Exam

This concept appears frequently in PMI exam questions about risk prioritization, especially in the Perform Qualitative Risk Analysis process. Questions test your ability to understand how the matrix determines risk priority, how scores are calculated, and how prioritization rules are established—either from organizational process assets or tailored to the specific project.

Key Points to Remember (for the exam)

• Purpose: Maps probability of occurrence against impact on project objectives to prioritize individual risks
• Scoring Method: Numeric values for probability and impact are multiplied to produce a probability–impact score
• Dual Representation: Opportunities use positive impact definitions; threats use negative impact definitions
• Priority Levels: Scores allow evaluation of relative priority within each priority level (e.g., high, medium, low)
• Prioritization Rules: Can be specified by the organization in advance (organizational process assets) OR tailored to the specific project
• Descriptive vs. Numeric: Both descriptive terms (very high, high, medium, low, very low) and numeric values are acceptable
• Common Confusion: Confusing qualitative scoring (probability × impact) with quantitative techniques like Monte Carlo analysis—the matrix is for qualitative risk analysis, not quantitative

Typical PMI Exam Example

A project manager is assessing risks for a software development project. The organization's risk policy defines probability as: 0.1 (very low), 0.3 (low), 0.5 (medium), 0.7 (high), 0.9 (very high). Impact is defined on a scale of 0.1 to 0.9. For a risk with probability = 0.7 and impact = 0.5, the probability–impact score is 0.35. This score places the risk in the medium priority level according to the organization's predefined matrix thresholds.

PMI Exam Traps

• Trap: Confusing the probability and impact matrix with quantitative risk analysis tools like Monte Carlo simulation or tornado diagrams

• Reality: The matrix is a qualitative tool used in Perform Qualitative Risk Analysis; quantitative techniques are separate and more detailed

• Trap: Assuming all organizations use the same scoring scheme or that scores are absolute values

• Reality: Prioritization rules may be specified by the organization in advance OR tailored to the specific project—there is no universal scoring scheme

• Trap: Forgetting that opportunities and threats use different impact definitions (positive vs. negative) but share the same matrix grid

• Reality: The same matrix can represent both, but impact definitions must be clearly distinguished

• Trap: Thinking the matrix determines the exact numeric value of risk exposure

• Reality: The matrix provides relative priority within priority levels, not absolute risk quantification

Important PMI Connections

Quick Review Questions

1. In the probability and impact matrix, how is the probability–impact score calculated when numeric values are used?

2. A risk is identified as an opportunity. How should its impact be defined in the probability and impact matrix compared to a threat?

3. Where can prioritization rules for the probability and impact matrix come from—are they always predefined by the organization?

4. What is the primary purpose of using the probability and impact matrix in qualitative risk analysis?

5. A risk has a probability of 0.3 and an impact of 0.7. What is its probability–impact score, and what does this score allow the project manager to determine?

PMBOK v8 Reference

Section 5 – Tools and Techniques, pages 187-188: "Example Probability and Impact Matrix With Scoring Scheme"

Note: The probability and impact matrix is a foundational tool in risk management. On the PMI exam, remember that it is used for qualitative prioritization, not quantitative analysis. Focus on understanding how scores are calculated, the distinction between opportunities and threats, and where prioritization rules originate.