Some baseball historians have long argued that pitchers have improved more than hitters, so that the pitching mound had to be lowered and the strike zoned narrowed in 1968 to give suffering batters a boost. Stephen Jay Gould, the Harvard geologist, zoologist and baseball pundit, has offered an evolutionary theory of baseball's hitting drought. The natural evolution of the game is that batters will tend to converge on a mean statistical average of about .260, with fewer at either extreme, Mr. Gould reasons. Mr. Schell's thinking is less abstract. He treats the question as an epidemiologist might, arguing that he can filter out all the major factors that influence a hitter's performance to isolate individual talent.
Several factors are straightforward to control.
He also lops off any hits in excess of 8,000 at-bats to free hitters of what might be called the Hank Aaron curse. Mr. Aaron played the game so long that his deteriorating skills in later years in some ways undermined his record-setting early years. The more complex part of the Schell formula takes a page from Mr. Gould. Mr. Schell agrees that hitting talent has tended to vary less over the years. In recent decades, he finds, a talent plateau has emerged.