Variability Risks and Event Risks


A brief guide

Practical Project Risk Management


By Martin Hopkinson

United Kingdom

Conceptualize risks so that they can be described, estimated and modelled appropriately.

Comparing Variability Risks and Event Risks

A Key Issue for Risk Management Practitioners

Project risk management activities are often based on the use of a risk register, with a probability-impact matrix (PIM) being used for the purposes of risk prioritization. The PIM technique lends itself to all risks being described and assessed as being event risks. In practice, this usually results in one of the following two approaches to variability risks:

  • Exclusion of variability risks from the risk register, or
  • Inclusion of variability risks by making estimates that force-fit them to the PIM.

The first approach is a practice error since many variability risks can be managed successfully if the relevant sources of uncertainty are identified and acted on.  Though not ideal, force-fitting variability risks may be the only practical choice for the process to address all significant risks.


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Editor’s note: This series of articles is by Martin Hopkinson, author of the books “The Project Risk Maturity Model” and “Net Present Value and Risk Modelling for Projects” and contributing author for Association for Project Management (APM) guides such as Directing Change and Sponsoring Change. These articles are based on a set of short risk management guides previously available on his company website, now retired. For an Introduction and context for this series, click here. Learn more about Martin Hopkinson in his author profile below.

How to cite this paper: Hopkinson, M. (2023). Variability Risks and Event Risks: A brief guide, Practical Project Risk Management series, PM World Journal, Vol. XII, Issue I, January. Available online at https://pmworldlibrary.net/wp-content/uploads/2022/12/pmwj125-Jan-2023-Hopkinson-Variability-risks-and-event-risks-series-article.pdf

About the Author

Martin Hopkinson

United Kingdom


Martin Hopkinson, recently retired as the Director of Risk Management Capability Limited in the UK, and has 30 years’ experience as a project manager and project risk management consultant. His experience has been gained across a wide variety of industries and engineering disciplines and includes multibillion-pound projects and programmes. He was the lead author on Tools and Techniques for the Association for Project Management’s (APM) guide to risk management (The PRAM Guide) and led the group that produced the APM guide Prioritising Project Risks.

Martin’s first book, The Project Risk Maturity Model, concerns the risk management process. His contributions to Association for Project Management (APM) guides such as Directing Change and Sponsoring Change reflect his belief in the importance of project governance and business case development.

In his second book Net Present Value and Risk Modelling for Projects he brought these subjects together by showing how NPV and risk modelling techniques can be used to optimise projects and support project approval decisions.  To learn more about the book, click here

To view other works by Martin Hopkinson, visit his author showcase in the PM World Library at https://pmworldlibrary.net/authors/martin-hopkinson/