Can You Accurately Estimate Coincidence Probabilities? | Self-Help - Psychology Today

This post was co-written with Dr. Magda Osman, an associate professor at Queen Mary University of London. 

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Bernard Beitman, M.D., visiting professor at the University of Virginia explains, New research shows that people can accurately judge whether an event is a coincidence or not—unless it happens to you. 

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Statisticians who study coincidences are fond of saying that ordinary people don’t know how to estimate the probabilities of coincidences. To illustrate our poor statistical thinking, statisticians trot out the Birthday Problem: How many people would have to be in a room to have a 50 percent probability that any two of them have the same birthday?

Non-statisticians do not confront problems like this in everyday life or when judging the probability of a coincidence. It’s a brainteaser that requires sophisticated mathematical reasoning.

The answer is a much smaller number than your intuition might guess: 23. Remember this is not about a 100 percent probability. It is a 50 percent probability. With two rooms of 23 people, on average one room would contain a  match. This is a tough problem to solve!...

Susan Jane Blackmore at the University of Plymouth and her colleagues have shown that people who tend to hold strong beliefs in the paranormal also tend not to be good at tests of probabilistic reasoning, or generating and spotting randomness in series of numbers. And a 2014 study by Robert Brotherton at Goldsmiths University of London and Christopher French at Goldsmiths University of London shows that people who hold strong beliefs in conspiracy theories tend to make more errors in understanding statistical concepts.

Magda Osman and colleagues (Mark Johansen Cardiff University, and Christos Bechlivandis University College London) have been working on several empirical investigations looking at people's coincidental experiences. In one of the projects, the task involved asking people to record their coincidences for periods of five weeks. The study did not define coincidences, instead it was left up to participants to decide what they considered coincidences to be for themselves. The idea was to look at coincidences in the wild rather than create fictitious coincidences to study, such as the birthday problem.
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Source: Psychology Today