Book Shows that Coin Tosses Are Still Not Random

August 17, 2009

Snap Judgment, David E. Adler's book about when to trust your instincts, reiterates something interesting about random walks.

Research into coin tosses has shown that there's more than mathematics that determines outcomes, and that the tosses aren't random. The upshot is that for natural coin flips by mere humans, the chance of a head coming up heads again is approximately 51/100. That is, heads facing up has a greater probability of heads; tails facing up predicts tails!

That's because when people flip coins there is a physical bias for the position the coins start out in. Coins flipped by humans tend to rotate around several axes at once. The phenomenon, called precession, has been investigated by mathematicians.

Stanford University’s Persi Diaconis and Susan Holmes, in collaboration with University of California, Santa Cruz mathematician Richard Montgomery, built a coin-tossing machine and filmed the action with a slow-motion camera, confirming that a machine could make tosses come out heads every time. Although the physics and mathematics behind their findings is complex, the basic idea is that when the force of two flips is the same, so is the outcome. You can, however, still read it for yourself in "Dynamical Bias in the Coin Toss" (SIAM Review, vol. 49, #2, pp. 211-35).

There is, perhaps, a simpler means of verification. See the coin tosses, and call the outcomes, in football games this fall!

Source: The Big Money.com, July 28