Statscape.(Baseball)

Every general manager--from the majors to your office fantasy league--would love to know how age affects player performance. Is that 30-year-old slugger in his prime or over the hill? How productive might he be in two years? Four years?

Baseball traditionalists hold that position players are in their prime from 28 to 32. Bill James--a founding father of sabermetrics and now a consultant to the Red Sox--has called this belief "blatantly false."

In his 1982 Baseball Abstract, James examined the career statistics of 502 hitters born in the 1930s and found that, on average, they had their best overall year at 27. He argued that players typically "attain their greatest value before the 28-32 period even begins, are declining throughout that age range and have lost nearly half of their peak value by the time it ends."

That view remains popular among sabermetricians and explains their alarm when Rangers second baseman Alfonso Soriano was revealed to be 28 rather than 26 after being traded by the Yankees for Alex Rodriguez. James' analysis hints that Soriano may be poised to slide rather than enter his prime.

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