Win Values Explained: Part Five
For the last couple of days, we’ve been talking about the different components of the Win Value system. However, you may have noticed that we’ve been dealing entirely in runs. wRAA, UZR, the position adjustment, and replacement level are all expressed in terms of runs, not wins, and that’s why the sum of those numbers is categorized under Value Runs.
So, if all of our metrics deal in terms of runs, but we want to get to wins, we need to know how many runs it takes to make a win. This is actually quite a bit easier than it sounds, thanks to the pythag formula for expected win-loss records. For those not aware of pythag, you can get a good estimate of a team’s winning percentage by dividing the square of runs scored by the sum of the square of runs scored and the square of runs allowed. Or, in formula terms:
RS^2/(RS^2 + RA^2) = Pythagorean Winning Percentage. So, if a team scored 775 runs and allowed 775 runs, they’d have a .500 Pythag Win%, or 81 wins and 81 losses – even amounts of runs scored and runs allowed should lead to something like an even record. Not as scary as it sounds.
What happens if we subtract 10 runs from the runs scored column, so that we now have a 765 RS/775 RA team? Pythag spits out a .4935 win%, and .4935 * 162 = 79.95 wins. So, instead of 81 wins, you’re now expected to win just barely less than 80. By subtracting 10 runs, you lost a fraction more than one win.
Same thing happens if you add 10 runs to the runs allowed column – 775/785 RS/RA spits out .4935 as well. How about if you add 10 runs, so we have a 785/775 team? .5064 win%, or 82.03 wins. Again, 10 runs added equals one win gained.
For an even more precise look at the issue, you could use the improved PythagenPat method, which places a better exponent in the calculation, but the conclusion is going to be the same; 10 runs = 1 win.
So, when you see value expressed in runs, but you want it in wins, just divide by 10. Likewise, if you see it in wins but you want it in runs, multiply by 10. It might sound like a cheap trick, but it’s reality – 10 runs add up to a win. A +20 run player is a +2 win player.
Dave is the Managing Editor of FanGraphs.
Not sure if there’s a part six, but you might want to throw in the run environment part of that as well–the translation for runs to wins changes slightly depending on the run environment.
I’m mostly trying to keep these basic enough for people who want to understand that the system works but aren’t going to try to re-engineer it on their own. So, I’m going to skip a lot of little details like that, and figure that for people who that kind of information matters for will look at the more in depth pieces written by guys like Tango.
That’s kind of too bad, David. I think we really suffer from being able to go to a place to understand these new stats (and you know how hard that is for me). Blog entries aren’t a good way to organize this content — that’s not what they’re meant to do. And if you’re only covering the “superficial” level of explanation, without at least links to more detail, that’s not as helpful as it could be.
I would suggest that, in your Glossary, you guys make a list of these blog entries, along with a list of blog entries that cover the details in more depth. I really think we need a central place that includes all the links to all the details, in a reader-friendly layout, in order to gain acceptance for your new stats.
Yea, we’ll end up doing something like that. I’m not trying to discourage discussion of the more in depth parts of the system, but was rather just saying that due to the nature of blog posting, I wasn’t going to be able to tackle everything in these write-ups.