<story><title>40k coin tosses yield ambiguous evidence for dynamical bias</title><url>https://www.stat.berkeley.edu/~aldous/Real-World/coin_tosses.html</url></story><parent_chain><item><author>mrandish</author><text>&amp;gt; A first comment is that it would have been better for each individual to have done both &amp;quot;Heads up&amp;quot;and &amp;quot;Tails up&amp;quot; tosses (which was part of the intended protocol, but on this aspect of the protocol there was a miscommunication)&lt;p&gt;That was a pretty unfortunate error in the experiment. Maybe it doesn&amp;#x27;t matter but now we don&amp;#x27;t know. It would also have been nice to have them swap coins halfway to expose any individual per coin biasing. It may seem like an irrelevant thing but I&amp;#x27;ve been a lifelong magician specializing in advanced slight of hand coin magic. I carry a set of coins with me all day, every day and handle them constantly. It started out as practice but evolved into both practice and a kind of fidget toy. I have sets of coins I&amp;#x27;ve probably handled for thousands of hours over decades.&lt;p&gt;Most people think of coins as immutable but they actually change quite a bit after hundreds of hours of handling. Most advanced coin magicians don&amp;#x27;t tend to use &amp;quot;trick&amp;quot; coins from a magic shop because they are actually too limiting. The coins I use are completely normal circulated coins but they are very specific because there are subtle differences in how coins handle which, at the most advanced levels, can matter. I have year-matched sets of coins I&amp;#x27;ve carefully assembled because they have the degree of surface wear (sometimes called &amp;#x27;softness&amp;#x27;) and edge-milling which works best for the style of slights I do. Coins also vary in shape and many aren&amp;#x27;t quite round. I&amp;#x27;ve actually hired a specialized machinist (aka coin-smith) to &amp;#x27;true-up&amp;#x27; the shape and then re-mill the edges of certain coins.&lt;p&gt;Based on my admittedly unusual experience in handling coins, I suspect that weight, edge and surface variations in individual coins could have a material aerodynamic impact at this statistical level (sub-half a percent). BTW, there are coin magicians who have mastered the ability to flip a normal coin and control the outcome to &amp;gt;95%. While the coin is normal in every way, it does need to be a coin they&amp;#x27;ve specifically trained with. Otherwise the hit rate falls considerably.</text></item></parent_chain><comment><author>the__alchemist</author><text>That&amp;#x27;s super interesting! Of note, the book Quicksilver (First book in the Baroque Cycle) goes into a few diatribes about subtle differences in coins in Europe a few hundred years ago; eg coins being valued by metrics other than their face value.&lt;p&gt;Eg:
&amp;gt; “I say, Daniel, is it true what they say, that those coins are perfectly circular?”&lt;p&gt;&amp;gt; “They are, Isaac—not like the good old English hammered coins that you and I carry in such abundance in our pockets and purses.”
...
&amp;gt;“if someone clips or files a bit of metal off the edge of a round coin with a milled edge, it is immediately obvious.”&lt;p&gt;&amp;gt; “That must be why everyone is melting those new coins down as fast as they are minted, and shipping the metal to the Orient…?” Daniel began,&lt;p&gt;&amp;gt; “…making it impossible for the likes of me and my friend to obtain them,” Isaac finished.&lt;p&gt;&amp;gt; “Now there is a good idea—if you can show me coins of a bright silver color—not that black stuff—I’ll weigh them and accept them as bullion.”&lt;p&gt;&amp;gt; “Bullion! Sir!”&lt;p&gt;&amp;gt; “Yes.”&lt;p&gt;&amp;gt; “I have heard that this is the practice in China,” Isaac said sagely. “But here in England, a shilling is a shilling.”&lt;p&gt;&amp;gt; “No matter how little it weighs!?”&lt;p&gt;&amp;gt; “Yes. In principle, yes.”&lt;p&gt;&amp;gt; “So when a lump of metal is coined in the Mint, it takes on a magical power of shillingness, and even after it has been filed and clipped and worn down to a mere featureless nodule, it is still worth a full shilling?”&lt;p&gt;&amp;gt; You exaggerate,” Daniel said. “I have here a fine Queen Elizabeth shilling, for example—which I carry around, mind you, as a souvenir of Gloriana’s reign, since it is far too fine a specimen to actually spend. But as you can see, it is just as bright and shiny as the day it was minted—”&lt;p&gt;&amp;gt; “Especially where it’s recently been clipped there along the side,” the lens-grinder said.&lt;p&gt;&amp;gt; “Normal, pleasing irregularity of the hand-hammered currency, nothing more.”</text></comment>
<story><title>40k coin tosses yield ambiguous evidence for dynamical bias</title><url>https://www.stat.berkeley.edu/~aldous/Real-World/coin_tosses.html</url></story><parent_chain><item><author>mrandish</author><text>&amp;gt; A first comment is that it would have been better for each individual to have done both &amp;quot;Heads up&amp;quot;and &amp;quot;Tails up&amp;quot; tosses (which was part of the intended protocol, but on this aspect of the protocol there was a miscommunication)&lt;p&gt;That was a pretty unfortunate error in the experiment. Maybe it doesn&amp;#x27;t matter but now we don&amp;#x27;t know. It would also have been nice to have them swap coins halfway to expose any individual per coin biasing. It may seem like an irrelevant thing but I&amp;#x27;ve been a lifelong magician specializing in advanced slight of hand coin magic. I carry a set of coins with me all day, every day and handle them constantly. It started out as practice but evolved into both practice and a kind of fidget toy. I have sets of coins I&amp;#x27;ve probably handled for thousands of hours over decades.&lt;p&gt;Most people think of coins as immutable but they actually change quite a bit after hundreds of hours of handling. Most advanced coin magicians don&amp;#x27;t tend to use &amp;quot;trick&amp;quot; coins from a magic shop because they are actually too limiting. The coins I use are completely normal circulated coins but they are very specific because there are subtle differences in how coins handle which, at the most advanced levels, can matter. I have year-matched sets of coins I&amp;#x27;ve carefully assembled because they have the degree of surface wear (sometimes called &amp;#x27;softness&amp;#x27;) and edge-milling which works best for the style of slights I do. Coins also vary in shape and many aren&amp;#x27;t quite round. I&amp;#x27;ve actually hired a specialized machinist (aka coin-smith) to &amp;#x27;true-up&amp;#x27; the shape and then re-mill the edges of certain coins.&lt;p&gt;Based on my admittedly unusual experience in handling coins, I suspect that weight, edge and surface variations in individual coins could have a material aerodynamic impact at this statistical level (sub-half a percent). BTW, there are coin magicians who have mastered the ability to flip a normal coin and control the outcome to &amp;gt;95%. While the coin is normal in every way, it does need to be a coin they&amp;#x27;ve specifically trained with. Otherwise the hit rate falls considerably.</text></item></parent_chain><comment><author>tash9</author><text>Well it&amp;#x27;s not like we&amp;#x27;re gonna run out of undergraduates, just do the experiment again.</text></comment>