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Fun With Numbers

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The six relievers who got the most playing time for the Mariners this year were David Aardsma, Sean White, Shawn Kelley, Miguel Batista, Chris Jakubauskas, and Mark Lowe. Here's how they did pitching to Rob Johnson and Kenji Johjima (Jak's starter stats are included because I didn't feel like separating them, but he conveniently threw to each catcher about equally often as a starter).

Johnson Johjima
uBB K HR PA uBB K HR PA
Aardsma 16 48 2 151 11 21 1 104
White 6 8 1 125 11 14 2 100
Lowe 9 32 3 153 12 26 3 130
Batista 15 17 1 106 21 30 6 175
Kelley 1 9 3 61 6 26 5 110
Jak 11 20 9 177 12 19 5 180
TOTAL 58 134 19 773 73 136 22 799
RATE 7.5% 17.3% 2.5% 9.1% 17.0% 2.8%

You'll see that, over remarkably similar sample sizes, the relievers walked fewer batters when throwing to Johnson than when throwing to Johjima. The other two stats aren't meaningfully different.

But wait! That's not a fair comparison, because the playing time distributions aren't the same for each catcher. For example, Johnson got to catch 50% more Aardsma, while Johjima had to catch 60% more Batista. What happens when you weight Johjima's numbers to equal Johnson's PT distribution?

Johnson: 7.5%, 17.3%, 2.5%
Johjima: 9.3%, 16.8%, 2.4%

There you go. Neither the strikeout nor home run rates are meaningfully different, and the walk rates are within two standard deviations of each other, but something to think about.