Does a "year of the pitcher" mean more 20-game winners?
"The 1968 season will always be the Year of the Pitcher ... Bob Gibson boasted a 1.12 ERA for the Cardinals ... Danny McLain won 31 games for the world champion Tigers ...
"[In 2010] there's an across-the-board dip in offensive statistics: through Sunday an average of 8.9 runs per game had been scored, down from the average of 9.3 through the same date last season. ... Home runs are in similar decline ...
"At week's end 15 hurlers ... were on pace for 20-win seasons; in the last six seasons there have been 12 20-game winners combined."
Ignore the obvious problem that there will always be more pitchers "on pace" for a goal than actually reaching it (for instance, there are lots of players "on pace" for a 162-home run season after one game). There's another thing there that didn't make sense to me: the idea that when pitching is up and batting is down, there will be more 20-game-winners than otherwise.
It makes sense for ERA, but not for wins. No matter how good or bad a league's hitting is, there is always the same number of wins to go around -- one per game played, or, in total, 162 times half the number of teams in baseball. Why should those wins be concentrated among fewer pitchers (which is what happens when you have lots of 20-game winners), just because the hitters are worse?
One explanation: perhaps hitters are worse because there are a bunch of great new pitchers and those are your extra 20-game winners. But that's not what's happening this year, is it? Even veteran pitchers are seeing their stats improve this year, aren't they?
So, maybe it's just a mistake, and SI didn't realize what they were saying. But, just to be safe, I checked. For every season since 1982 (except 1994), I counted how many pitchers won 20 games, and calculated the league ERA. (Actually, I mean the *MLB* ERA, not the "league" ERA. But that sounds awkward. Is there a better way to say it?)
Then, I ran a regression. And, to my surprise, the correlation was significant (p=.04). The higher the ERA, the fewer 20-game winners. For every 0.37 increase in overall ERA, there was one fewer 20-game winner that season.
Leaving out 1995 made the result a bit less significant (p=.06) but kept the effect size about the same (+0.42 ERA gives one less 20-game winner).
So what's going on?
Here's one possibility: managers are failing to adjust for the higher offense, and are going to the bullpen too soon. In a low-scoring league, a pitcher having a bad day might give up four runs in the first five innings, but stay in the game. In a higher-scoring league, he might give up five runs, and be lifted. The manager doesn't quite adjust enough for the fact that the two performances are equivalent. As a result, some of the wins that would go to the starter wind up going to the bullpen instead.
There's a better alternative, one that doesn't have to assume managers are irrational. It could be pitch counts. Suppose a starter stays in for 100 pitches. In a high-offense league, a starter's 100 pitchers lead to five runs in four innings. In a lower-offense league, the 100 pitches yield five runs in five innings. The low-offense starter gets the win; the high-offense starter doesn't.
In any case, I don't know which of the two explanations is right. It could be a combination of both. Or can anyone think of other explanations?