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Fair coins tend to land on the same side they started

arxiv.org

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Re: Fair coins tend to land on the same side they started

#91

Post by mewpmewp2 »

kibwen wrote: post #78
kqr wrote: post #35

Earlier quoted context omitted.

> That's amazing, but I guess it won't help when the person can choose the bias? Alice writes on a piece of paper whether to use the result from the first or the second coin, Bob flips the coins however he likes, then once there are two different sides of the coins up, Alice turns over the paper and reveals to Bob which coin contains the result. Though I guess that unnecessarily complicates the procedure – maybe Alic…

At this point you can just play odds and evens: one person picks odd, the other picks even, they both hold up either one or two fingers behind their back, reveal them at the same time, then sum the result. This prevents the randomness from being in any one actor's control. If you're worried that your brain's RNG can be gamed, then put an odd-denominated coin in one hand and an even-denominated coin in another, and mi…

We still need a study then to confirm that when people try to mix the coins in their hands like that, it would be random enough. And that would take another year...

Re: Fair coins tend to land on the same side they started

#93

Post by misja111 »

helsinkiandrew wrote: post #85

I think you can argue that the experiment wasn't representative of 'normal' coin flips. On average, each flipper in that experiment flipped a coin over 7000 times, after that amount many people will have learned to flip in a comfortable way with less variance between physical action and force they use. I'd imagine that in that case the coin would more likely land with the same orientation. I don't think this would be…

I bet that with enough practice, you can learn to toss the coin so that you get a much bigger than 51% chance of landing it on the same side.

Re: Fair coins tend to land on the same side they started

#94

Post by glandium »

nomilk wrote: post #83
fbartos wrote: post #2

About a year ago, we embarked on a quest to answer one of the most intriguing questions: If you flip a fair coin and catch it in hand, what's the probability it lands on the same side it started? Today, we are finally ready to share the results. Thanks to my friends, collaborators, and even strangers from the internet, we collected flippin 350,757 coin flips. We ran several "Coin Tossing Marathons" (e.g., https://you…

It becomes clear why there's a same-side bias when watching the video: https://www.youtube.com/watch?v=3xNg51mv-fk These are fairly gentle coin tosses; barely going a foot into the air! When I think of a coin toss, I think high and spinning fast (like the ones before sports games, where the coin goes into the air and lands on the ground, usually rolls a short way, and is collected on whatever side it landed). I would…

With a 1 foot to 2 feet toss, landing in the hand, I can get the same side as the starting side more than 90% of the time, without even trying. I wouldn't trust such a toss to be fair. Landing on the floor would change the game.

Re: Fair coins tend to land on the same side they started

#95

Post by rax0m »

I watched one of the 12-hour coin tossing marathons.

They were sitting with their laptops and pressed a button for every result.

I wonder if human error can explain (at least part of) the deviation from 50/50:

* locations of the buttons they pressed on the laptops (they only pressed once per toss before enter, meaning the button represented same-side or other-side)

* remembering what the coin started out as may be harder (or easier, but probably harder) when the result is other-side

* other??

Need to repeat this amount of tosses but with a higher degree of supervision to be sure of the result.

Re: Fair coins tend to land on the same side they started

#96

Post by mewpmewp2 »

saalweachter wrote: post #50
mewpmewp2 wrote: post #34

Earlier quoted context omitted.

Alert: It's not going to be as simple as this to make money even with large numbers. So don't fret about not having the money and missing some golden opportunity. There are enough actors out there trying to develop complex algorithms to find an edge, and so there wouldn't be any simple edges like this left anywhere as they would be arbitraged away. If there is a simple pattern, it is noticed and traded until the patt…

Also, if you do find an edge, you need to be prepared for what happens when everyone else discovers your arbitrage opportunity, and/or you tap out the potential of it. A number of failed finance companies have the story: find a legitimate arbitrage opportunity; take on a billion dollars in investment to exploit the opportunity; make bank; other people discover your arbitrage opportunity and jump on; stop making bank;…

Stock market is such a slippery addiction slope. With casino a reasonable person would know, the odds are stacked against themselves, but with Stock Market, there's no guarantee and it's really easy to convince yourself that you have an edge, and sometimes it works for a while, and then it doesn't, but you are already used to that feeling of reward, and as you said you will start to engage in riskier and riskier opportunities to get that feeling back.

Re: Fair coins tend to land on the same side they started

#97

Post by bob88jg »

098799 wrote: post #84
ChocMontePy wrote: post #69

Earlier quoted context omitted.

If anyone wants to test it, someone wrote a short code that simulates doing that 100,000 times: https://www.techiedelight.com/generate-fair-results-biased-c... The coin is biased to come up TAILS 80% of the time, but using Von Neumann's method in the program I got HEADS 50.035%, TAILS 49.965%.

Why would you test it? Probability of two heads: p*p Probability of two tails: (1-p)*(1-p) Probability of head followed by tails: p*(1-p) Probability of tails followed by heads: (1-p)*p It's not difficult to notice that if you remove the first two, the last two form a 50/50 distribution

Why would you not - analytical solutions are the rare occurrences might as well approach everything with simulation...

Re: Fair coins tend to land on the same side they started

#99

Post by dataflow »

jbandela1 wrote: post #16

Von Neumann described a very elegant way to get fair results from a biased coin. 1. Flip the coin twice 2. If you get the same result both times, goto 1 3. Now that you have different results for your pair of flips, use the first element of the pair of flips as your result. https://en.wikipedia.org/wiki/Fair_coin#Fair_results_from_a_...

I'm confused, how does this help? If coins are biased to land same-side up, then don't I always have an advantage by guessing whatever side is up before the first throw?
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