What is Probability and Impact Matrix?
The probability-impact (P×I) matrix is the grid that turns qualitative risk scores into priorities: probability on one axis, impact on the other, each cell colored by severity. Risks land in cells; the red corner gets response plans, the green corner gets a watch list.
Its quiet prerequisite is calibrated definitions — "high impact" must mean the same dollars and days to everyone scoring, or the matrix ranks opinions, not risks.
Formula
Risk score = probability rating × impact rating
Worked example
A tunnel project defines the scales first: "high impact" = >$2M or >30 days. Sixty identified risks score into the grid; seven land red (including groundwater inflow at the fault zone), and only those seven get funded response plans and named owners. The matrix's real product isn't the coloring — it's the defensible decision to ignore forty-five green risks without guilt.