“People don’t understand probabilities” – or do they?

Weather forecasting science has long been developing ensemble forecasts as a way to improve forecast capability and provide better information to support users’ decisions. The science is well proven and the Met Office will soon move to an ensemble-only NWP (Numerical Weather Prediction) system. Ensemble forecasts can be used in a number of ways, but fundamentally they provide a probabilistic picture of the weather forecast which includes a most likely outcome but also information on the confidence, uncertainty or risks associated with forecast outcomes. In order to pull through the full benefits of this information it is important to communicate this information effectively to as many users as possible so that they can make appropriate risk-based decisions. There is a widely-held belief that people will find probabilistic information hard to understand or make use of – “People don’t understand probabilities” – which provides a significant obstacle to communicating it.

This challenge for ensemble forecasts has long been recognised and there has been extensive research conducted into effective communication and people’s understanding of such forecasts. This paper offers a review of that research to help guide future communications of forecasts. The overwhelming and consistent conclusion found in the literature is that people do understand the probabilistic information and make better decisions when presented with it, provided that the information is presented appropriately.

The literature review provides strong support for communicating probabilistic information to forecast users, including the general public. It does not support the idea that people’s understanding should be a barrier to communicating such information. While not every single person will understand or take full advantage of the additional information, most people will benefit and make better decisions as a result.