League differences in the 1950’s

If you look at the batting statistics of Willie Mays and Mickey Mantle at their peaks, it is obvious to anyone with the slightest familiarity with sabermetric techniques that Mantle was the superior hitter at his peak. Of course, Willie Mays was the better fielder and both his peak year period and total career was far longer than Mantle’s.
Just as a hitter though, in their best 3,4,5 (or however you want to define it), Mantle accounted for more runs (about 15 per year by my baseruns calculations) while using fewer outs – about 80 or enough to be worth another 15 runs.
But what if Mays, playing in the national league, was facing tougher competition than Mantle was in the american league? I don’t remember where I heard this first, but it seems to be accepted as conventional wisdom now. The question is, is this really true, and if so, how big? Are we talking about knocking 5 runs a year off Mantle or enough to make their peak offensive seasons equal?

I went to the Lahman database and looked at every hitter who played in both leagues during the decade of the 1950’s. I used the matched at bat method, a player with 600 at bats in the NL and 75 in the AL counts at 75, and so on, and calculated runs created for each group of players. Players who in the American League created 3.97 runs per 27 outs created 4.26 per 27 during their time in the National League. Not what I expected. I then looked at pitchers and found that pitchers who 4.47 runs per 9 innings in the American League allowed 4.79 in the NL. Exactly the opposite conclusion, but this would make sense if the leagues were equal in quality but the National League had better hitters parks, or strike zones that made it more of a high scoring league.
But if I look at total run scoring they are about even, 4.46 for the AL and 4.48 for the NL. Since the pitcher and hitter differences are of the same magnitude, and pointing in opposite directions, I have to conclude that they are inconclusive. I see no strong evidence that one league was stronger than the other during this decade.
A few other points:
The hitters and pitchers who changed leagues were worse overall than league average. There was no free agency, so the really good players, for the most part, were not changing leagues.
While a big explanation for the NL being stronger is that the NL was quicker to integrate, perhaps this was balanced somewhat by the best team in baseball, the Yankees, being in the AL. With only 8 teams, the Yankees accounted for 12.5% of the AL’s talent level, one team could have more of an effect than that they could in today’s 14-16 team leagues.
While the Yankees could not buy free agents, there was no amateur draft and the Yankees were able to assert their dominance by signing the best youngsters and stockpiling their minor leagues.

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5 Responses to League differences in the 1950’s

  1. JoeArthur says:

    could you elaborate a little on your method? I assume you didn’t limit yourself to comparing totals of players who changed leagues within the same year. Did you look for any asymmetry in the age of the players or their home park effects before and after changing leagues?

  2. Sean Smith says:

    I looked at players who played in both leagues over the whole decade. I’m just assuming that if your sample is large enough, you should cancel out park and age effects.

  3. MGL says:

    There are some issues that you have to be aware of and account for when looking at players who switch leagues. One is that, as Sean says, they tend to be players who have had bad seasons, so the next year, they will be better by regression toward the mean. Two, is that there is probably a familiarity affect, which was probably more pronounced in pre-FA and pre-IL eras, whereby pitchers do better for a while after switching leagues and batters do worse. I had to deal with these issues when I was doing my research on comparing the current and recent differences between leagues. Having more star players in one league, or something like that, should not really matter in looking at the data, as long as all of players you are looking at face a cross section of opponents, in aggregate of course. You are just trying to figure out if there are any differences between the average hitter or average pitcher between the leagues. It does not matter if a few players bring up or down the average or if any differences are because of a lot of players, again, as long as all players are pretty much repreented (there are no biases) among the opponents of the players who switch leagues.

  4. fggf says:

    Doesn’t Mantle playing on the yankees aid his stats by some as well as his league not intergrating as fast?

  5. Sean Smith says:

    I’m sure not having to face Yankee pitching helped Mantle somewhat.

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