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April 18, 2006

Prospectus Today

Confirmation Bias

by Joe Sheehan

As expected, the Toronto Blue Jays are scuffling, playing .500 ball through two weeks and hanging around at the bottom of a deep AL East. Their $100 million investment in pitching has yielded just ten innings of work so far, as A.J. Burnett has made only one start while B.J. Ryan pitches about as often as a modern closer does. The back end of the rotation has suffered from the winter’s defensive downgrades, especially Josh Towers, who’s allowed 25 hits in 12 2/3 innings. The offense is averaging six runs a game, but that’s not sustainable--they’re not going to hit .321 all year. Look for the Blue Jays to stay within a handful of games of .500 throughout the season, and be disappointed by their final record.

Out in Oakland, the A’s are off to an unimpressive 6-7 start, albeit one that has them tied for first in the AL West. They’ve allowed more than five runs a game, a figure that belies a stat line showing them to have the highest strikeout rate in the AL, a better than 2-to-1 strikeout-to-walk ratio, and the fourth fewest home runs allowed in the league. That 5.26 ERA is going to fall, and when it does, the A’s will get separation in the West on their way to a division title.

The two paragraphs above are factually accurate, deceptively analytical…and a load of crap.

I’m a bit dogmatic on the idea of not drawing conclusions off of small sample sizes. The statistical reason is that baseball performance, by both teams and players, can vary widely over the course of the season. Two weeks of play simply isn’t enough time for the underlying ability to shine through the variance, rendering the data essentially unusable.

The stickier problem, though, is confirmation bias. Confirmation bias is the very human tendency to assign importance to the data that fits our hypothesis, and dismiss the data that undermines it.

The Blue Jays are off to a .500 start and playing lousy defense behind a contact staff? That’s to be expected when you overspend on so-so free-agent pitchers and trade away a great glove man like Orlando Hudson. And that six runs a game they’re scoring (in part due to acquired-for-Hudson Troy Glaus and his 1037 OPS)? That won’t last. The A’s, however…their 6-7 start isn’t something to be taken seriously. The core talent is very good, and they’ve just been unlucky in how many runs they’ve allowed in the early part of the season.