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Probability and Impact Matrix

The probability and impact matrix is a grid that maps the probability of a risk occurring against its potential impact on project objectives, producing a risk score used to prioritize risks.

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Explanation

The probability and impact matrix (P&I matrix) is a key tool in qualitative risk analysis. It combines predefined probability ratings (e.g., 0.1, 0.3, 0.5, 0.7, 0.9) with impact ratings on a similar scale. The intersection of a risk's probability and impact values yields a risk score, which determines whether the risk is categorized as high, moderate, or low priority.

The matrix is defined in the risk management plan, including the scales, thresholds, and color-coding (often red/yellow/green). Separate matrices may be created for different project objectives such as cost, schedule, scope, and quality, since a risk might have high impact on schedule but low impact on cost.

Risks in the high-priority (red) zone receive immediate attention—detailed analysis, response strategies, and dedicated risk owners. Moderate (yellow) risks are monitored and may have contingency plans. Low (green) risks are placed on a watch list and reviewed periodically.

Key Points

  • Combines probability and impact ratings to produce a risk score
  • Defined in the risk management plan with scales and thresholds
  • Separate matrices may exist for cost, schedule, scope, and quality
  • Categorizes risks into high, moderate, and low priority zones

Exam Tip

Know how to calculate a risk score: Risk Score = Probability x Impact. A risk with P=0.7 and I=0.8 scores 0.56, which typically falls in the high-priority zone.

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