Is a coin toss fair ?
You may find the answer to be rather surprising ... no.
http://www.stat.berkeley.edu/~aldous...in_tosses.html The mathematical proof is found: http://comptop.stanford.edu/u/preprints/heads.pdf A coin is more likely to land as it started (not accounting for you flipping it at the end, in which case it would be the opposite). I think this is important because coin tosses are a popular and sometimes official method (sports) of "fairness". |
But wouldn't the fairness be restored if no party knows the starting conditions? AFAIK, you decide for one side before the coin is tossed, before knowing the starting conditions.
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I used to practice flipping coins so that I had a very good chance of getting heads or tails depending on the starting position. I'm sure a professional (ie magician) could do it nearly 100%. Just be careful who you flip with and how ;)
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Does the coin land on the ground or does one catch it and "flip it over" as some do?
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Catching it may be the best thing to do. If it falls on the floor and bounces this is ok, but if it rolls or spins then that adds a huge amount of bias due to the uneven weight distribution of the coin.
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As a side note, dice may also show bias if they have even small imperfections in manufacturing:
http://www.awesomedice.com/blog/353/...s-gamescience/ I would say that casino dice are better to use if you are actually gambling (like in a casino) http://dicephysics.info/0107.htm |
I particularly liked linked page since it gives lots of approaches to what data to gather. Also the main article tells what further analysis can be done with the data.
http://www.stat.berkeley.edu/~aldous...ugrad_res.html OK |
How many shuffles do you think it takes to randomize a new deck of cards ?
http://www.ams.org/samplings/feature.../fcarc-shuffle |
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I must try to teach myself again. |
Half the time it is fair I'd guess.
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The article notes that it hasn't been proven empirically, and mentions the time needed to do a useful number of flips. That sounds like a job for distributed experimentation to me - anyone for Flipping@Home?
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A coin-toss is theoretically "fair," but no coin is fair, and coin tossers can certainly train themselves to cheat you. Just as can any dealer in a casino, no matter what precautions "the house" might take to prevent it. (As if "the house" actually would . . . ) Yes, they can cheat you, and no, you will not see it being done.
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