June 09, 2004

» Heads I win, tails you lose

Diaconis next coaxed Ali Ercan, an electrical engineering doctoral student in El Gamal's lab, into helping collect the data. For each coin flip, they wanted at least 10 consecutive frames -- good, crisp images of the coin's position in the air. From these sequences they would derive the angular momentum vectors they needed to describe, in quantitative terms, the coin's complicated motion.

[...]


Preliminary analysis of the video-taped tosses suggests that a coin will land the same way it started about 51 percent of the time. "It's a gem-like example of what we know that isn't so," Diaconis says. Though a skeptic since childhood, he believed that "if you flipped a coin vigorously, it was going to be fair.

"But it's not so bad," he says. "One in a hundred is pretty close, actually. It gives me faith that probability assumptions can be validated and useful, but you have to look at them case by case."