How do you create a biased coin? With pliers!
Via Mike Izbicki, who teaches mathematics at Claremont McKenna College (CMC), coin “0” pictured above is unbiased, but coins 1 through 6 were bent to various degrees using a pair of pliers. Professor Izbicki conducted Bernoulli trials on all seven coins, tossing each one 100 times. Below are his raw results:
Prof Izbicki wrote up his mathematical analysis of these results here. In brief, his ultimate conclusion is as follows: “Amazingly, it takes some pretty big bends to make a biased coin. It’s not until coin 3, which has an almost 90 degree bend that we can say with any confidence that the coin is biased at all. People might notice if you tried to flip that coin to settle a bet!”