I've seen some of his postings and even participated in debates with him in other message boards. He seems reasonably smart, but appears to lack formal training in statistics, so none of the numbers he cites are any more sophisticated than conditional sample means. He has a lot of these numbers at his fingertips, and that seems to impress the average layperson. He also has a tendency to bend the numbers to suit his biases.
Statistics almost never answer questions - they just help you ask the right questions.
Bill James is the only baseball stats guy I've been impressed with. It isn't compiling the stats that's impressive - it's being able to relate them to the game. Bill James knows enough about baseball (the game on and off the field, not the box score), and baseball history, that he can usually put the statistics he compiles into perspective.
In fact, statistics usually only play a minor supporting role in his best articles.
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