Slashdot Mirror

← Back to Stories (view on slashdot.org)

Science of the coin-toss: Bias in Heads-or-Tails

Posted by CmdrTaco on from the didn't-gildenstern-prove-that-already dept.

MrSharkey writes " An interesting article published in Science News puts a new scientific spin on the outcome of the venerable coin-toss. "A new mathematical analysis suggests that coin tossing is inherently biased: A coin is more likely to land on the same face it started out on.""

4 of 559 comments (clear)

  1. This is interesting... by WordUpCousin · · Score: 5, Interesting

    A coin is more likely to land on the same face it started out on.

    If this is true, we would still want to call the opposite face since we after it lands, we always flip it onto the other hand. That is, if we start with heads facing up, and it lands more frequently with heads facing up on our palms, by the time we slap it onto the back of our opposite hands, tails is facing up!

  2. Re:Oh Darn... by Anonymous Coward · · Score: 5, Interesting

    In football games they let the coin hit the ground and bounce around before coming to a stop. That introduces complexities that the scientific study did not address.

    It may very well turn out that the odds of getting heads/tails after letting the coin fall on the ground are still 50-50.

  3. Avoiding bias by geophile · · Score: 5, Interesting

    There is a neat trick for dealing with a biased coin in a coin toss:

    - Flip twice.
    - Discard the pair of throws if it's both heads (HH) or both tails (TT).
    - Count HT as heads, and TH as tails.

    (I think this idea was from John von Neumann.)

    Applied to the current situation: Flip twice, once starting H down, once with T down.

  4. Re:Butter-side down by mcmonkey · · Score: 5, Interesting
    The reason bread usually lands butter side down has to do with how it falls off a counter.

    Scientific American actually crunched the numbers on this issue a couple years ago for a piece on Murphy's Law. Turns out the universe is out to get you.

    Considering the case of a slice of bread slipping off the counter top, it will begin to rotate at that point the center of gravity is off of the counter. Presuming a fall from rest and you're not spiking your bread, the rate of fall and rotation are determined by gravity.

    Your main variable is this case is the height of the counter top. Although it turns out this height is constrained to a narrow range of comfort determined by human physiology.

    Now take this argument to the general case of an arbitrary bipedal on an arbitrary planet. The most probable height of humanoid-type life is a function of gravity on the home world. Planets with weaker gravity make it easier to grow taller people; conversely planets with stronger gravity will tend to produce shorter people.

    The taller beings have higher counter tops, but the weaker gravity will cause their bread to rotate slower than our earth-bound bread. Turns out their counter tops will also be at a height destined to produce butter-down drops.

    Same for the munchkins on the planet with stronger than earth gravity. Their bread will rotate fast enough to make it around to butter-side-down when falling from their munchkin-height counter tops.

    So yes, the fundamental laws governing the universe are designed to ruin your breakfast. Look on the bright side, it's not just you--the universe is out to get everyone.