Tuesday, February 10, 2015
Bias in age calculations
?There are two ways to take the average of a number: the right way and the wrong way.
The wrong way is to take a series of number, truncate them, then average them. You can see that in many places, but I'll just pick one at random the 2014 Tigers pitchers. The age listed is the pitchers age as of June 30, truncated. So, if a pitcher is 28 years and 1 day or 28 years and 364 days as of that date, he's 28 years old. That's called truncation. That's the age that is listed there. If you take the weighted average (weighted by IP), you get an average age of 28.1 years old. Which is the second problem, that after you truncate a number, you can't then add a significant digit.
Someone can do the calculation for me, but I would bet on the true average age as of June 30 to be right around 28.6 years old. There's a 6 month bias because of the truncation issue. I've been talking about this for as long as I can remember. And no one else seems bothered by the fact how much math gets hurt.
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