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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

#151

Earlier quoted context omitted.

You can solve this easily by always flipping with the same side (doesn’t matter which) facing up for all flips.

There is skill to coin flipping. You'd need to blind the flipper, either physically blindfold or make it so they don't know which result is the positive outcome ahead of time.

Or ask the competitors to flip the coin in a manner they doesn’t allow for skill, like put it in a Yahtzee cup and toss from there.

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

#152
post #56

I always tell people that result of coin flip is highly start state dependent. Imagine a sequence of H(ead), T(ail), H, T, H, T, ... if the sequence starts with H first, in no way can the number of T exceed that of H, but the number of H might be 1 greater that that of T. I never tested my self, but I hypothesize that the propability will be more skewed if the number of revolutions is less, i.e. having a shorter Head…

If I were to dig through my comment history I would find I have already responded to this exact sort of comment before, so let me regurgitate :)

If the coin is resting on your hand waiting to be flipped, it is currently mid-way through being on side up. This is because the switch between being e.g. heads up to tails up is done when the coin is vertical. If it isn't a clear explanation, try imagining catching the coin and "flattening" it at different angles, while 50% of angles will match either side, at the moment the coin is flipped, it is already half-way through the angles representing the current side.

This means that the correct sequence you describe it not THTHTH but rather THHTTHHTTHH. Taken at even intervals, both sides will appear the same number of times. Taken at odd intervals, at half of the intervals there are more Ts and the other half have more Hs.

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

#153
post #97
post #84

Earlier quoted context omitted.

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...

You learn a lot more from generating an analytical solution than a simulation, so it's usually worth at least taking a stab at it analytically before jumping to monte carlo methods.

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

#154
post #113

Earlier quoted context omitted.

But they need to remove the possibility of a psychological guessing game. E.g. Bob could've researched before hand that people are 55% likely to pick heads if they can pick by themselves.

That doesn’t remove the possibility of a psychological guessing game, just makes it more convoluted. If Bob knows Alice will pick first, he can still bias the results.

Inconceivable!

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

#155

Earlier quoted context omitted.

> Why would you test it? I recall conversations on Usenet decades ago about the Monty Hall problem[1] in which people gave elementary proofs that probabilities don't change by opening a door. Even from mathematicians and statisticians. People were very insistent that the analytical solution was simple and obvious and that switching doors didn't change anything. The only thing that changed some people's minds was a pr…

You can demonstrate the Monty Hall problem solution analytically with Bayesian statistics using prior probabilities, no need to go all the way to Monte Carlo methods.

As a proof the math is entirely sufficient, but for those who may struggle with it the simulation is persuasive.

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

#156
post #126

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_...

With all due respect to Von Neumann, intuitively I would change it to use the information in the two coins: one for (X, Y) and another for (Y, X). Not the first.

Yes, and as the second coin carries no information (because we are focusing now on sets of two different consecutive outcomes) both your and JvN's protocols are equivalent.

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

#157

Earlier quoted context omitted.

The probability of [HEADS, TAILS] is always the same as the probability of [TAILS, HEADS], no matter how the coin is weighted.

I get that but I don't see how it answers my question?

You're flipping pairs of coins until you get either "HT" or "TT". So the only two possibilities are:

1. keep flipping until you get HT (and so you choose 'heads') 2. keep flipping until you get TH (and so you choose 'tails')

Since HT and TH are equally likely, results 1 and 2 are equally likely, i.e. there's a 50% chance of choosing heads, 50% change of choosing tails.

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

#158
post #84

Earlier quoted context omitted.

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 test it? I recall conversations on Usenet decades ago about the Monty Hall problem[1] in which people gave elementary proofs that probabilities don't change by opening a door. Even from mathematicians and statisticians. People were very insistent that the analytical solution was simple and obvious and that switching doors didn't change anything. The only thing that changed some people's minds was a pr…

This was how I built an intuition into the Monty Hall problem as well! Wrote a little app that simulated it a decade or so ago when I was discussing with friends!

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

#159

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_...

That's amazing, but I guess it won't help when the person can choose the bias? Because according to the study the person can choose the bias by choosing which side start up. So if the person wants tails based on what you've said, they should always 1. Do the first throw starting tails up. 2. If the first one is tails, then they now want to start second one heads up. 3. If the first one is heads, they will want to try…

But wasn't the bias in the paper something like 50.5% vs 49.5%?
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