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

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399 points seanhunter | 9 comments | 19 Nov 24 09:03 UTC | HN request time: 1.053s | source | bottom
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acyou ◴[19 Nov 24 17:23 UTC] No.42185920[source]▶
The paper looks like it has a large sample size, but it actually has a sample size of only 48 testers/flippers. Some of the videos of those testers show very low, low-rpm coin tosses, we're talking only 1-2 flips. Where they also flipped thousands of times, presumably in the same way. So there is actually a very small sample size in the study (N = 48), where testers that don't flip properly (low rpm, low height, few coin rotations) can affect the results disproportionately.

Doesn't look like the study author backgrounds are particularly focused on statistics. I would presume with 48 authors (all but 3 of which flipped coins for the study), the role of some might have been more test subject than author. And isn't being the subject in your own study going to introduce some bias? Surely if you're trying to prove to yourself that the coins land on one side or another given some factor, you will learn the technique to do it, especially if you are doing a low-rpm, low flip. Based on the study results, some of the flippers appear to have learned this quite well.

If the flippers (authors) had been convinced of the opposite (fair coins tend to land on the opposite side from which they started) and done the same study, I bet they could have collected data and written a paper with the results proving that outcome.

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1. salt4034 ◴[19 Nov 24 17:43 UTC] No.42186149[source]▶
> testers that don't flip properly

I think that's the point. It shows that people don't usually flip properly, leading to biased results.

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2. fluoridation ◴[19 Nov 24 17:49 UTC] No.42186225[source]▶
But is that the case? The only way I've ever seen people flip a coin is by flicking it in the air with their thumb and either catching it or letting it hit a surface. I've never seen someone flip a coin like it was a die.
3. lcnPylGDnU4H9OF ◴[19 Nov 24 18:22 UTC] No.42186573[source]▶
There is a [video presentation of the paper](https://www.youtube.com/watch?v=-QjgvbvFoQA) which does a good job of explaining the inspiration for the study within the first few minutes.

It sounds like what they were intending to study is the actual variance that is introduced, on average, by imperfections in throws conducted by humans. Unless that's mistaken, it's a fair point to consider the n=48 here. Did they discover an average that can be generalized to humans or just to those 48?

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4. arandomusername ◴[19 Nov 24 18:26 UTC] No.42186611[source]▶
Except that flipping a coin hundreds/thousands of time in a row is not a representive of how people will flip a coin a single time/few times.
5. chongli ◴[19 Nov 24 18:26 UTC] No.42186614[source]▶
Yes and what immediately jumps out to me as a source of bias is that they asked this small group of 48 coin flippers to flip thousands of times each. I would’ve thought it would be obvious that when you ask people to do something thousands of times they might do it in a different (and biased) way than someone doing that thing only once.

Get a hundred thousand people to flip a coin once each and then see what happens!

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6. fluoridation ◴[19 Nov 24 19:08 UTC] No.42186986{3}[source]▶
What's more, from the numbers cited it sounds like they had 48 people do nothing but flip coins for 8 hours (avg. 15 flips/min). Whether continuous or with breaks, there's no way you won't become seriously consistent. 7000 flips is many more flips most people will perform in their entire lives.
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7. dfxm12 ◴[19 Nov 24 19:53 UTC] No.42187402{3}[source]▶
Get a hundred thousand people to flip a coin once each and then see what happens!

Of all the stats we collect in sports, I wonder if someone has info on coin tosses in sports like American Football, Tennis, etc. I wonder if there are even rules regulating how a coin should be tossed in different sports...

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8. dylan604 ◴[19 Nov 24 19:58 UTC] No.42187453{4}[source]▶
In some circles, they'd make a post about how their "AI" flipped a coin 8000 times.

Waiting for the HNer that likes electronics hacking to Show HN: My coin flipping robot I built over a weekend for consistent flips.

9. skykooler ◴[20 Nov 24 13:00 UTC] No.42193559{4}[source]▶
Having stats on the outcome of coin tosses in sports wouldn't help, because it's unlikely that the state of the coin before flipping was recorded.