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Study indicates coin flips are not exactly 50/50

University of Amsterdam researchers analyzed the results of 350,757 coin flips and determined coins had a 50.8% chance of landing on the same side they started from. Photo by jarmoluk/Pixabay.com
University of Amsterdam researchers analyzed the results of 350,757 coin flips and determined coins had a 50.8% chance of landing on the same side they started from. Photo by jarmoluk/Pixabay.com

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April 2 (UPI) -- A team of researchers analyzed the results of 350,757 coin tosses to determine whether the results are truly 50/50, and found "fair" coins are slightly more likely to land the same way they started.

Franti?ek Barto?, a researcher at the University of Amsterdam, led a team that analyzed the results of 350,757 coin flips from 48 people using 46 currencies.

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"We found overwhelming evidence for a 'same-side' bias predicted by Diaconis and colleagues in 2007: If you start heads-up, the coin is more likely to land heads-up and vice versa," Barto? wrote in sharing his results on social media.

He said his team found that coins flipped into the air and caught in the hand had a 50.8% chance of landing on the same side they started from.

The study, titled "Fair coins tend to land on the same side they started: Evidence from 350,757 flips," was published online.

"If you bet a dollar on the outcome of a coin toss (i.e., paying 1 dollar to enter, and winning either 0 or 2 dollars depending on the outcome) and repeat the bet 1,000 times, knowing the starting position of the coin toss would earn you 19 dollars on average," the researchers wrote.

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"This is more than the casino advantage for six-deck blackjack against an optimal-strategy player, where the casino would make $5 on a comparable bet, but less than the casino advantage for single-zero roulette, where the casino would make $27 on average," the paper states.

Barto? said his team also found the odds varied slightly from flipper to flipper, with some coin flippers showing a clear bias toward same-side landings and others showing no bias at all. He said this can be explained by slight variations in flipping techniques.

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