Sunday, July 05, 2009
Baseball Games Not Independent: Streaks Maybe Real!
It was long thought by stats nerds that streaks in sports were not real, or at least could be attributed to chance. Any sports fan down to his or her core of course believes in hot hands, hot bats, etc. The statisticians made their argument based on a statistical analysis that assumed that each game was independent of the next. However, it was recently shown by some dude named, Trent Macadder (who I can't find on the Internet), that the games themselves are not independent. This lack of independence throws all the stats out the window, and streaks may again be beyond what can be explained by chance--at least according to the awesome podcast, Radio Lab.
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3 comments:
It looks like it's "McCotter". As somebody who knows a little something about statistics and next to nothing about sports, I always thought streaks were (at least sometimes) real. First, it makes total sense for the underlying construct (say, a player's ability to hit a baseball) to change over time, including over very short intervals. Why wouldn't it be affected by things like mood, fatigue, adrenaline, etc.?
Second, it's far too easy for statisticians to confuse a model for reality. To say "a model assuming independence of outcomes fits the data" isn't the same as "the outcomes are independent."
Third, although a stochastic model might work well for modeling a complex process, arguably there is no randomness in many sports processes. Take (switching sports) free throws. All parameters - the weight and size of the ball, the distance to the basket, the angle and amount of force needed to propel the ball - are (intuitively) knowable. Delivering the proper amount and angle of force is difficult, but it isn't random. You could argue that ability to do so _is_ random; but the claim that the probability of doing so is constant is a much stronger, harder-to-justify claim.
Non-independent outcomes?
Obviously this is a case for Francesca!
The first thing she will do is require you to focus....
"First, it makes total sense for the underlying construct (say, a player's ability to hit a baseball) to change over time, including over very short intervals."
This is often noted by the anti-streak crowd as something you and I and the rest of the amateurs see as self-evident but may not be true among *professional* athletes who have spent years and years perfecting consistency in their approaches/motions. If a robot were tasked to hit a baseball I imagine it would not be streaky, and a robotic style is arguably the goal of most hitters/throwers/golfers/shooters/etc.
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