Flipping a Coin

Flipping a coin may not be the fairest way to settle disputes. About a decade ago, statistician Persi Diaconis started to wonder if the outcome of a coin flip really is just a matter of chance. He had Harvard University engineers build him a mechanical coin flipper. Diaconis, now at Stanford University, found that if a coin is launched exactly the same way, it lands exactly the same way. The randomness in a coin toss, it appears, is introduced by sloppy humans. Each human-generated flip has a different height and speed and is caught at a different angle, giving different outcomes. But using high-speed cameras and equations, Diaconis and colleagues have now found that even though humans are largely unpredictable coin flippers, there's still a bias built-in, if a coin starts out heads, it ends up heads when caught more often than it does tails. NPR's David Kestenbaum reports.