Baseball offers perhaps the world’s richest data set: pretty much everything that has happened on a major-league playing field in the past 140 years has been dutifully and accurately recorded, and hundreds of players play in the big leagues every year.

Baseball people believed they knew the answers to those questions, and all the others. But those assumptions hadn’t been tested in decades, if ever, so it shouldn’t be surprising that many of them turned out to be wrong. From that gap between the assumed and the actual, Beane and his assistants were able to use their limited budget to construct