# Coin Toss NOT Fair

We toss a coin and ask people to name either "heads" or "tails" because we think this gives each side an equal chance?except it doesn't. Statistician Persi Diaconis says, "I don't care how vigorously you throw it, you can't toss a coin fairly."

Erica Klarreich writes in Science News that Diaconis' mathematical analysis shows that coin tossing is biased, because a coin is more likely to land on the same face it started out on. The only way a coin toss can be fair is if you throw it so that it that it spins perfectly around a horizontal axis through its center?which is impossible. The worst kind of toss is when the coin stays flat and doesn't flip at all. This toss guarantees the coin will land on the same face it started out on. Most coin tosses are somewhere in between the two, but Diaconis' math team found that all of these are biased.

It's actually hard to tell, just from watching a toss, whether or not a coin has flipped, since a coin toss only takes about half a second. "Sometimes we had the complete impression that the coin had turned over when it really hadn't," says fellow investigator Susan Holmes.

Mathematician Joseph Keller thinks magicians and hucksters take advantage of this. He says, "Some people can throw the coin up so that it just wobbles but looks to the observer as if it is turning over." During World War II, South African mathematician John Kerrich tossed a coin 10,000 times while he was in a German prison camp. But since he didn't record which side he started on, he never discovered this bias.

Is the question of whether UFOs are real a toss-up? Not if you read Confirmation. It's been called the best review of UFO and abduction evidence ever written.

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