[kqr]

> 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 Alice can just write "heads" or "tails" on a note and then Bob flips without having seen the note. It essentially replaces the second coin with Alice's mind which hopefully doesn't suffer from the same known bias.

[sebzim4500]

If you're going to go that way you can skip the coin flip entirely. Just get both of them to write heads or tails on a note and then compare. This technique is used in some crypto projects, except instead of writing on a note you share cryptographic commitments.

[mewpmewp2]

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.

[arijun]

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.

[CuriouslyC]

Inconceivable!

[kibwen]

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 mix them up so that even you don't know which hand has which.

[InitialLastName]

I can feel the difference between denominations of my local coins no problem. What you need are a pair of coins with an odd year imprint and an even year imprint.

[mewpmewp2]

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...

[mewpmewp2]

Suppose Alice needs to take the coin first to herself, to use the aforementioned strategy without intentionally introducing bias, and then using result of that, which would determine whether the first or the second result from Bob would be used. Because otherwise Bob may be able to make psychological "guesses".

[amluto]

There are nice protocols like this that don’t require anyone to visibly flip a coin. See, for example:

https://en.m.wikipedia.org/wiki/Commitment_scheme

[c22]

° Put the coins in a cup

° Shake the cup vigorously and dump coins on the table

° If coins match, go back to step one

° If coins are opposed take the result of the southernmost coin