Risk-based thinking – it’s risky not to understand the mathematics of risk (and randomness)

Dr Melvyn Langford explains how the US Department of Defense (DoD) invented the 5×5 risk matrix in the 1980s.

Risk Assessment Guide & Template Collection

The methodology uses ordinal numbers (which are only for ranking) as if they are suitable for calculations.  It is misleading, meaningless and gives erroneous risk ratings that result in great waste.

In 2003 the DoD issued new guidance acknowledging this.  IEC/ISO 31010 began to cash in with improvements in 2009.  However the 5×5 matrix is still in widespread use, including in the NHS.

By using uncalibrated rankings as if they had a linear relationship, the matrix badly over-estimates potential problems.  This leads to major financial waste.

What do UKAS have to say about the matrix?

“When assessing risks, are UKAS expecting to see a risk matrix of likelihood and impact similar to how health and safety risks are assessed?

o ISO/IEC 17011:2017 and UKAS are not prescriptive of how risks are documented.”

To see the tables and graphs read the article on p39-45 of Health Estates Journal, May 2019.


This entry was posted in History, Laboratory medicine, Management, NHS, Practical problems, Science and tagged , , , , . Bookmark the permalink.

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