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Fair coins tend to land on the side they started (2023)

(www.researchgate.net)
392 points seanhunter | 3 comments | 19 Nov 24 09:03 UTC | HN request time: 0.471s | source
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japoco ◴[19 Nov 24 15:17 UTC] No.42184331[source]▶
This is probably just because the coins aren’t actually fair. If the coin is slightly biased towards heads, the first throw is more likely to heads, and so are all subsequent throws. Same for tails.
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Vecr ◴[19 Nov 24 15:20 UTC] No.42184385[source]▶
That's not the problem. You can test that by using a highly secure random number generator, e.g. /dev/random in Linux, to select the initial side. Keep track of that initial side, record the side it lands on. This paper shows a same-side bias, not a heads bias.
replies(1): >>42184497 #
japoco ◴[19 Nov 24 15:27 UTC] No.42184497[source]▶
A same side bias is either a heads bias or a tails bias.
replies(2): >>42184551 #>>42184611 #
alt227 ◴[19 Nov 24 15:31 UTC] No.42184551[source]▶
Its not, its a bias towards which side the coin started on.
replies(1): >>42184586 #
1. japoco ◴[19 Nov 24 15:33 UTC] No.42184586[source]▶
Which is either heads or tails.
replies(2): >>42184964 #>>42185041 #
2. glxxyz ◴[19 Nov 24 16:04 UTC] No.42184964[source]▶
A coin with a heads bias is more likely to land on heads no matter how it's thrown.

A coin with a same side bias is more likely to land on heads if it's thrown with heads facing up, and more likely to land on tails if thrown with with tails facing up.

3. toast0 ◴[19 Nov 24 16:12 UTC] No.42185041[source]▶
If you take a specific coin and find that when you prepare it to be flipped showing heads up, that it is more likely to land heads up, and that when you prepare it to be flipped tails up, it is more likely to land tails up, it seems confusing to call that coin 'heads or tails biased'