Originally Posted by

**brett**
There is a problem with ERA+. The average of two ERA+ scores is not the composite ERA+. For example if a player has a 200 ERA+ for one season (200 IP) and 100 for the next season, their ERA+ is not (and should not) be 150. It will be 133. This is because the average of reciprocals is not the same as the reciprocal of averages. If instead we see that his RA- (I would prefer to call it relative RA) would be 0.50 for one season and 1.00 for another then the average of those (as well as the composite) would be 0.75. (which would correspond to an ERA+ of 133).

I guess I would take RA9/RA9avg off of baseball reference to get relative RA for a pitcher. Take 1 minus that number to get the runs saved ratio. So say a guy has a 0.8 relative RA+, he would be saving 0.2 games worth of runs per game. Multiply that by innings and divide that by 9 to get games worth of runs saved. If you double that, you should get something that is very similar to WAA, though with one win being worth 2x the run environment.

You could also find WAA by using a pythagorian estimate based on RA-. If a player has an RA- (or relative RA) or 0.8, their team (if average) would win 1/(1+.8^2) proportion of their "games" that he pitched. That would be 0.609. Multiply that by innings divided by 9 and then subtract 0.5xinnings/9 to find how many wins he netted his team.

Would you even want to average it though? All of the weights would be different, so wouldn't you want to just recalculate?

"Batting stats and pitching stats do not indicate the quality of play, merely which part of that struggle is dominant at the moment."

-Bill James

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