I’m 100% Certain About That….
I’ve just arrived home after being away for work all week. For almost all of the two hour drive home, I was tracking parallel to storm clouds all around me, and on the radio, the broadcast was regularly interrupted with ‘weather alerts’ warning of severe storms in my area.
When I arrived home I checked out the weather radar application on my phone and sure enough it seems that storms are tracking my way. I then checked my weather forecasting application, and not surprisingly, it is predicting storms over the next few hours. Not only is it predicting storms to happen, it is suggesting that there is 100% chance of them occurring (check out the photo with this story).
This got me thinking about what 100% ‘chance’ actually means? Do this mean that rain will definitely fall in all of areas in which I live during all of the times that it is predicted?
I wonder whether we really understand the numbers that we use so regularly in prediction, particularly in risk? Could it be that everyone may not understand these numbers in the same way? If we don’t all have the same understanding of the references that we use when communicating about risk, what does this mean when we agree on a risk score? What impact may this have on how we deal with, and understand risk?
This reminded me of a story shared by Gerd Gigerenzer in his book Risk Savvy:
“The probability that it will rain on Saturday is 50 percent. The chance that it will rain on Sunday is also 50 percent. Therefore, the probability that it will rain on the weekend is 100 percent.” (Gigerenzer, 2014, p.4)
Gigerenzer then goes on to note about this story:
“Most of us will smile at this. But do you know what it means when the weather report announces a 30 percent chance of rain tomorrow? 30 percent of what? I live in Berlin. Most Berliners believe that it will rain tomorrow 30 percent of the time, that is for seven to eight hours. Others think that it will rain in 30 percent of the region; that is most likely not where they live. Most New Yorkers think both are nonsense. They believe that it will rain on 30 percent of the days for which this announcement is made; that is, there will most likely be no rain at all tomorrow” (Gigerenzer, 2014, p.4)
I remember when I first read this story that it resonated with me. I considered how relevant this is in risk and safety. We use numbers and percentages all the time to evaluate, assess, analyse and to attempt to understand risk all the time. But do we have a common understanding of what these numbers and percentages mean? Gigerenzer further notes that:
“Left on their own, people intuitively fill in a reference class that makes sense to them, such as how many hours, where, or how heavily it rains. More imaginative minds will come up with others” (Gigerenzer, 2014, p.4)
I wonder how this may play out in risk and safety?
I refer finally to Gigerenzer when he sums this up nicely when referring to the latest weather forecasting technology, by suggesting:
“But greater precision has not lead to greater understanding of what the message really is. The confusion over probability of rain has persisted in fact since the very first time there were broadcast to the public in 1965 in the US. The confusion is not just limited to rain, but occurs whenever a probability is attached to a single event.” (Gigerenzer, 2014, p.4)
Gigerenzer’s advice to readers is “Always ask for the reference class. Percent of what?”
I wonder whether Gigerenzer can help all of us in risk and safety to become more risk savvy. The question is, are we prepared to explore these questions or are we stuck in blissful ignorance believing that everyone is thinking in the same way about risk? Do we need better and more meaningful conversations with each other in order to better understand what we mean when talking about risk?
Update; its just hit 5.25pm and it isn’t raining yet. I guess that means that 100% does not mean it will rain during 100% of the time that it was predicted. I wonder what it does mean though?
There’s a chance we might get rain tonight……
We’d love to hear your thoughts, experiences and comments.
Author: Robert Sams
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FIRST PUBLISHED ON http://www.safetyrisk.net