Interesting article caught my eye today:

Ball? Strike? It Depends: Is the Pitcher an All-Star?

By NICHOLAS BAKALAR—JULY 7, 2014—N.Y. Times
They would rather not talk about it, but umpires may be just as star-struck as the average baseball fan. Two researchers looked at the photographic evidence and found that umpires make more errors in favor of All-Star pitchers than pitchers who have never been selected for an All-Star Game — about 17 percent more. This is a subject umpires are naturally hesitant to discuss.
“I don’t know the science,” the umpire Fieldin Culbreth said, sipping a bowl of soup as he prepared for a game between the Mets and the Oakland Athletics. “And I wouldn’t understand it even if you tried to explain it to me. I umpire from here and here,” he said, indicating his head and his heart.
Mike Winters, who has been a major league umpire for 24 years, put it simply: “I wouldn’t expand the strike zone for anyone.”
But the science exists, for anyone who wants to look at it. Every major league stadium is equipped with the Pitch f/x system, which includes strategically placed cameras that record the locations and trajectories of every pitch. The technology provides a record that is difficult to dispute. In the seasons the study covered, 2008 and 2009, umpires earned a B-plus average, at best, in calling balls and strikes.
The researchers — two business school professors, Jerry W. Kim of Columbia Business School and Brayden G. King of Northwestern’s Kellogg School of Management — looked at data on 756,848 pitches over 313,774 at-bats in 4,914 games. Some umpires were, unsurprisingly, more accurate than others, but on average they called a strike on 18.8 percent of pitches that were actually out of the strike zone and a ball on 12.9 percent of pitches that were, in fact, strikes.
Many factors besides All-Star status could affect an umpire’s judgment, so the researchers adjusted for the home team advantage, the importance of the at-bat to the outcome of the game, the count at the time of the pitch, whether the pitcher or the hitter was a lefty or a righty, the catcher’s ability to frame a pitch and make a ball look like a strike, and even the size of the crowd.
But after controlling for all these variables and more, the advantage gained by a pitcher’s status was still large. For each additional appearance in an All-Star Game there was a 4.8 percent increase in the probability that an actual ball would be called a strike. A player with five All-Star appearances had a 14.9 percent chance of a true ball being called a strike, which is a 16.7 percent increase over the chance a journeyman will benefit from the same mistake.
The error is not just the result of All-Stars being around the plate more than other pitchers. Even on the identical pitch just outside the zone, All-Stars got the call when journeymen did not.
With miscalled strikes, the same thing happens in reverse. A pitch in the strike zone thrown by a journeyman has a 19 percent chance of being called a ball. For the All-Star, the probability drops to 17 percent. That may not seem like a lot, but it means that an All-Star gets an automatic 9 percent advantage based not on his performance but on his reputation.

Although the effect is somewhat weaker, the same kind of bias appears when an All-Star batter is at the plate. The researchers calculate that a five-time All-Star has roughly a 5 percent or 6 percent advantage in getting a favorable ball-strike call.
The suspicion that the stars are treated differently by umpires is widespread among both players and fans, but until now it has been based on anecdote and rumor.

That there are numbers to support the belief came as a revelation to some players.
“I’m surprised at that,” the Mets’ Bobby Abreu said when told of the finding. Then he started to think. “Well, most All-Star pitchers are always around the plate,” he said, “so most of the time they’re going to get credit for a strike. Umpires know who’s on the mound.”
Al Clark, who umpired in the major leagues for more than 25 years before his retirement in 2001, said that on the contrary, umpires pay no attention to who’s who. “We don’t see who’s pitching; we don’t see who’s hitting,” he said. “We have to make a snap decision on what we see.”

And yet a few minutes later, Clark acknowledged that pitchers known for their control are in fact treated differently. “If a pitcher is throwing strikes, then it’s accepted that the zone is expanded,” he said. “If he’s not, he’s got to throw a defined strike.”
Mets reliever Vic Black is a pitcher who is likely to be a victim of the bias. “Really?” he said. “You mean the rich get richer? I never really thought about that. I just try to throw the ball over the plate. I know a lot of umpires miss a lot of my calls; sometimes they give me one.”
Mets starter Jon Niese was more sympathetic than shocked. “It’s still a human back there,” he said, “so they make mistakes.” He paused for a beat. “But if you’re going to give anyone the benefit of the doubt,” he added, “it’s going to be somebody like Adam Wainwright.”
The study does not name any names, but Wainwright, the Cardinals’ ace, is the kind of All-Star who would get the called strike that others would not.
Kim, the Columbia professor, said others were probably also given an advantage. “I suspect that players like Justin Verlander or even Koji Uehara would benefit quite a lot,” he said, naming Detroit’s ace and Boston’s closer.
“I hope no one takes this as an indictment of umps,” he said. “As fans, we should still appreciate what the umps are doing and realize that the biases are something everyone shares. It’s not that umps are incompetent, or deliberately benefiting the All-Stars for some reason. It’s human. It’s natural.”
And, he added, the numbers have improved in recent years. “Right now, it looks like the mistake rate is around 9 to 10 percent for false strikes; 5, 6 percent for false balls. It does seem to be the case that umpires have gotten better. But there are subtle biases that are very hard to correct.”