Morlidge's Little Book of Operational Forecasting (part 7 of 8)


Book CoverNote: Following is an eight-part serialization of selected content from Steve Morlidge's The Little (Illustrated) Book of Operational Forecasting.

The measurement challenge

So here is the forecasters dilemma:

There will always have forecast error. The challenge is to work out the cause of the error and to take the appropriate action based on this knowledge. This means determining whether error is due to:

  • The forecasting model being wrong - which would require it to be changed or recalibrated
  • A temporary or permanent change in the behavior of the system being forecast – which might require a new model or for the existing one to be supplemented with judgement
  • Noise – which cannot be changed, so the correct course of action is to do nothing

In practice, all these factors are jumbled up together and can vary enormously in size and impact.

Forecast error taken in isolation will never tell you how good a forecast is and what should be done to improve performance, because an unknown proportion of it will be unavoidable noise.


Don’t waste time on unavoidable error. The key to good forecasting is to work out how much error is avoidable, why and what to do to reduce it.


Coming Next: Good forecasts don’t always look right

People often interfere with forecast processes because they believe that they can tell how good a forecast is likely to be based on visual inspection…whether ‘it looks right’. This lesson explains why we cannot rely on our intuition.


About Author

Mike Gilliland

Product Marketing Manager

Michael Gilliland is author of The Business Forecasting Deal (the book), and editor of Business Forecasting: Practical Problems and Solutions. He is a longtime business forecasting practitioner, and currently Product Marketing Manager for SAS Forecasting software. Mike serves on the Board of Directors for the International Institute of Forecasters, and received the 2017 Lifetime Achievement in Business Forecast award from the Institute of Business Forecasting. He initiated The Business Forecasting Deal (the blog) to help expose the seamy underbelly of forecasting practice, and to provide practical solutions to its most vexing problems.

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