Ordinal Scaling

Ordinal Scaling is a method of ranking data into ordered categories where the relative position of each item is meaningful, but the precise differences or intervals between categories are not equal or quantifiable. In risk assessments, it is applied to likelihood and consequence ratings on scales such as 1–5 or verbal descriptors (e.g., Rare, Unlikely, Possible, Likely, Almost Certain), enabling risks to be plotted on a matrix and prioritised by their ranked position.

Examples include:

• Rating the likelihood of a chemical spill as “Possible” (score 3) versus “Likely” (score 4) on a 5-point ordinal scale without defining exact probability percentages
• Scoring consequence severity as “Major” (4) on a 1–5 matrix where the difference between Moderate and Major is subjective rather than measured in dollars or fatalities
• Using colour-coded risk matrices (green–yellow–red) where red is ranked higher than yellow, but the numerical gap between them is arbitrary

The concept of ordinal scaling is widely used in HSEQ, project risk management, and compliance frameworks such as ISO 31000 to provide a simple, consistent way to prioritise risks when detailed quantitative data is unavailable or impractical.

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