Is He Ready For the Show?

Your starter goes down with an injury. Your bench player's defense isn't offsetting the pathetic bat that he carries. Your setup pitcher blows his third straight game and your patience is at an end. Any number of things can drive us GMs to the madness that is trying to decipher AAA stats and how they might translate into the big leagues. Today we'll take a look at Major League Equivalencies in the ABL.

Equivalencies, first introduced by Bill James, are a way of comparing performances across environments. They tell you what a players stats would be comparable to if they played in a different league or time. In my calculations, I targeted two specific stats wOBA, already discussed by Alex, and FIP, a measurement of events that pitchers can control - walks, strikeouts, and home runs, scaled to an ERA like number. The numbers noted here are not 100% accurate because they haven't been park-adjusted, and in some cases omit some of the smaller or unavailable statistical categories such as IBB or reaching base on error. If I can find the pertinent data, I will adjust these results, but until then they can be used as a good approximation.

To build the Equivalencies, I pulled the stats of all the players who accumulated either 100+ PA or 30+ IP in both AAA and the ABL. I compared the rate stats (vs IP or BF) for the groups performances at the ABL level against their rate stats at the AAA level. Unsurprisingly, for hitters their H/PA, 2B/PA, 3B/PA, and BB/PA rates all decreased, while their K/PA rate increased. Pitchers saw their BF/IP, H/BF, HR/BF, and BB/BF increase and their K/BF decrease. After finding the % changes in these rates, I determined how it would affect the player's wOBA or FIP.

The results: batters experienced an approximate 21% decrease in their wOBA when they transitioned to the majors while pitchers saw an almost 36% increase in their FIP. With the stats that are available on a league wide basis, the league average wOBA was 0.334 and the league average FIP was 4.20. Based on the calculations I made, a hitter must be putting up a wOBA of 0.424 in AAA to be comparable to an average ABLer, while a pitcher must have an AAA FIP of 3.09 to be comparable to an average ABL hurler.

I'll be continuing this process with transitions between AA and AAA, and between A and AA. The combined sets of Equivalencies will allow you to see what kind of numbers you could expect out of your 18yo tearing the cover off the ball in A if you promoted him all the way to the big leagues.