Coin Tosses Are Not 50/50: It may come down to the tosser

You’d assume that as coins have two sides and you introduce a random element (flipping the coin and catching it), the odds of it coming up with your pick is 50/50 (or one in two). But researchers have crunched the numbers, looking at an impressive 350,757 coin tosses, and found that coin tosses are not 50/50 after all. You can tip the odds ever so slightly in your favor.

According to one team led by American mathematician Persi Diaconis, when you toss a coin you introduce a tiny amount of wobble to it.

“According to the Diaconis model, precession causes the coin to spend more time in the air with the initial side facing up,” a new team writes in a pre-print paper that has not yet been peer-reviewed. “Consequently, the coin has a higher chance of landing on the same side as it started (i.e., ‘same-side bias’).”

Diaconis found, from a smaller ideal number of coin tosses recorded and analyzed, that coins land on the same side they were tossed from around 51 percent of the time. The new team recruited 48 people to flip 350,757 coins from 46 different currencies, finding that overall, there was a 50.8 percent chance of the coin showing up the same side it was tossed from.

Delving into the data further, they found that coin tosses are highly variable between people, with some showing a strong same-side bias and others having none at all – coin tosses may come down (ever so slightly) to the tosser.