Earlier this week we did a post on survivorship bias, and how it could trick people into believing in psychic ability. It turns out that the most famous test of psychic ability was made expressly to allow for this kind of bias.
One of the most famous tests of psychic ability was made by J. B. Rhine. He claimed to identify strong psychics by testing a lot of people with Zener Cards. The tests involved two people, the examiner looking at the card, and the person being tested trying to guess the card that the examiner is looking at. Rhine noted that some people, a small minority, got a disproportionate number of cards right. They were "strong psychics." Skeptics countered that, if you were to test any group on the street, some would do far better than average - just as some would do far worse than average. That's the point of survivorship bias. You test a large amount of people and hold up the few who do better-than-average as examples of proof rather than coincidence.
One could argue that there shouldn't be a coincidence at all. What are the chances that if someone looks at a card - a card that could show any picture at all - that another person will be able to guess the picture on it? The chances, it turns out, got a lot better once Zener Cards were invented. Zener Cards were made by Karl Zener, a paranormal investigator.
The card trick was old, but up until the turn of the century, people just used playing cards. People had to guess, using their psychic abilities, what number and suit was on the card. This was a problem, because under controlled conditions, and a fifty-two card deck, pretty much no one got it right. Zener cards are comparatively simple. There are five cards - a circle, a square, a star, a cross, and wavy lines - repeated five times in a deck. Every time you guess you have a one out of five chance to get it right, and if you can count cards, your odds get better and better as you go.
In other words, the psychic test itself is an example of survivorship bias. Using regular cards would prove that no one was psychic. (Or, at least, not psychic in that way.) So the test had to be modified until it was possible for some people to be "proved" psychic through coincidence alone.
Top Image: David Blanch