Flooding the Return Period
What does finding someone who shares your birthday, and a 1:100 storm have in common? They both happen more often than you’d expect. In fact, once there are 23 people in a room, you’ve got as much chance of guessing a coin-toss as finding two people born on the same day. That’s probability for you, about as intuitive as a rock in the face- or something like that.
The cynic in me notes that the Return Period phrasing seems designed to dismiss the event as impossible to predict, whilst giving the client the impression that it’ll never happen again.
Having enjoyed my wettest cycle of the year (yes, I know we’re only nine days in); I had good cause to reflect on the irony of having experienced so many “1:100” year storms during my lifetime- while ringing out my socks into the cistern. Perhaps the greatest concern is that the more “1:100” year rains I cycle through, the more likely I am to get equally soaked- confused yet?
The “1 in X” year description of an extreme event is an odd one (know as a Return Period). The cynic in me notes that the phrasing seems designed to dismiss the event as impossible to predict, whilst giving the client the impression that it’ll never happen again. In fact, I sincerely hope that Wikipedia’s article on the subject is accurate when it credits Civil Engineering for the terminology.
In an attempt to demonstrate the wonderful world of Return Periods, I’ve made this little widget. The graph shows the probability of a “1 in X” year event happening over a period of years. By moving the slider you can can change the return period and see how it affects your chances.
Despite everything, however, Return Periods should give hope to all those searching singles; despite there only being a 63% chance that you’ll meet that one “once in a lifetime” person, there’s a 1 in 5 chance that you’ve already met them.
Isn’t probability wonderful.