The random coin toss must be one of society’s most frequently used decision-making mechanisms. We use the coin toss to choose which movie to see, to determine team positions in major sporting events, to divvy up household chores, and even name cities. But it may be that the the random coin toss isn’t so random. A 2007 study found that a vigorously flipped coin is likely to land on the same side it started on at least 51 percent of the time, possibly more depending on the person doing the flipping. (HT: Chris Blattman)[%comments]
Not So Random After All
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@Ari: My dad was able to win EVERY TIME if he flipped the coin and you called it in the air. How? By catching the coin and manipulating it as he slapped it onto the back of his other hand.
You can only negate this by letting the coin fall onto the ground.
I’m not sure I understand the title of this column.
What you say is that: “a vigorously flipped coin is likely to land on the same side it started on at least 51 percent of the time.”
This statement doesn’t imply that the process is not random; you’re saying that the toss is not necessarily independent of the starting conditions, which is completely different.
The implication is that the probabilities of heads or tails have some dependence on the starting conditions.
“Not so random” should really be replaced by “Not so independent” or “Not so unbiased.”
@Peter Bouman: You’re right… using the statistical definition of “random”, the biased coin toss is still random. However, the vast majority of the public doesn’t understand the technical definition and uses “random” to mean something like “all outcomes have equal probability”.
wow- this makes no country for old men that much more profound…
#2 Walter
Makes you wonder why the NFL depends on overtime to decide games at all, the NCAA system is much more equitable.
Persi Diaconis (the first author on the paper), the colorful coin-tossing, card-shuffling mathemagician has been studying this stuff for decades. My Stanford roommate had him a couple years back for stats; word on the street is he has trained himself to toss a heads every time. Made me wonder if he was in fact that missing 1%.
Random? Just ask Rosencrantz.
I read about a study not too long ago which sounds a lot like this study (I’m not sure if it’s really the same one since I am having trouble loading the pdf linked here.)
In the study I refer to, the reason for the coin landing more often on the side it started was because every once in a while the coin failed to flip at all, even though it looked like it was flipping.
The way this happens is that the coin “wobbles” in much the way that a coin spun on a table would. This causes the coin to look like it is flipping when it is not. Some magicians who control coin flips may have simply learned to reproduce this behavior.
Most of the coin flips in the study that I read about were actually performed by a coin-flipping robot and the “wobble” effect was confirmed by watching slow-motion video of coin tosses.
While there are certainly people who can manipulate their own coin tosses (possibly by using reproducing the “wobble” behavior) I do not think that that this study’s results were influenced by a rogue magician getting into the sample.
Concerning the method of having one person flip and the other call, this would only eliminate advantage if the caller couldn’t see the initial up-side of the coin.