Repeat ad nasuem: (insert name of Yankees SP) has pitched better to (insert name of Yankees backup catcher) than he has to Jorge Posada this year. 

Because of this, Jose Molina will be starting against Minnesota tonight, because A.J. Burnett's numbers with Jorge Posada behind the dish (6.1 IP per start, 5.33 Runs Allowed/9 innings) are far worse than they are with the trio of backup catchers the Yankees have employed this year (6.4 IP per start, 3.42 RA/9). 

We all know the basic question that's fueling this debate: is Burnett pitching better because Molina/Cervelli/Cash is catching, or is it just a happy coincidence, kind of like how I haven't contracted the Swine Flu or West Nile Virus ever since I moved into my new house four months ago?

I looked at Burnett's season, start by start and, quickly, it became pretty clear that not all of Burnett's troubles can be attributed to who's catching. 

Look at Burnett's stats vs. Boston this year:

And then look at him vs. the rest of Major League Baseball:

In a word, ouch.  Whether it's due to bad luck, poor pitching, coincidence, or whatever, Burnett has fared horribly against Boston this year, and has pitched very well against everyone else.  But guess what? Jorge Posada caught all four of Burnett's starts against Boston, from his 5 inning, 9 run stinker on August 22nd to his 7 2/3 inning, 0 run gem on August 7th. 

Now, we don't know why Burnett pitched poorly against Boston in three of his four starts.  Maybe it's because Posada only called one good game.  Maybe it's because Burnett was exceptionally wild and didn't have command of his stuff.  Maybe it's because Boston is a really, really good hitting team.  Either way, when a pitcher gives up 5 walks, 5 hits, and 5 runs in 2 2/3 innings (see 6/9 vs. Boston) it probably doesn't matter who's catching, yet if you exclude those four starts, Burnett's RA/9 with Jorge behind the dish drops by over a full run.

This whole argument, about who should catch, who calls a better game, and Catcher's ERA, can be easily skewed by small sample sizes. You need proof?   There are 37 catchers who caught at least 100 innings in the American League this year.  Twelve of them managed to catch 50% of their team's innings.  You know what?  Of those twelve, eleven had a Catcher's ERA that was within +/- 10% of their team's overall ERA.  Of the remaining 25, only 11 had a Catcher's ERA that was within +/- 10% of the team's actual ERA. 

The point?  Most teams have a mix of pitchers ranging from good, to mediocre, to bad  (see 2009 Yankees, C.C. Sabathia, Mariano Rivera, Joba Chamberlain Chien-Ming Wang, Sergio Mitre).  The more innings a catcher squats behind the plate, the more likely he is to get the full mix of the good, the bad, and the ugly.  But when he's on DL for an extended period of time, only plays day games following night games, or spends part of the season in the minors, he's far less likely to catch the full range of pitchers who might see game action in a given year. 

Jose Molina caught 357 innings this year, the equivalent of about 40 games.  In truth, if 40 games meant anything in the long run, we'd still be talking about how the Blue Jays had a better record than seven of the eight playoff teams (they did through 40 games this year) or how Raul Ibanez slugged .737 (through 40 games, he did).  The truth is that 40 games don't mean much of anything in the long term, not when you're trying to make sound judgments about players and teams. 

And so here's the only comparison that I care about. Since 2002, when he became a semi-regular catcher, Jose Molina has caught 3,725 innings, about 32% of his teams' total, with a Catcher's ERA that is 4% lower than his team's total ERA during that stretch.  Posada has caught more than twice as many innings - 7,725 - during that stretch, 67% of his team's total, with a Catcher's ERA that is 3% higher than the team's overall ERA.

So Posada's CERA is 7% higher than Molina's relative to their team's average, and that's before you consider that a 32% sample carries a lot less weight than a 67% one.  The point is, I'm not convinced at all that Catcher's ERA is a meaningful statistic, or that any one particular catcher has a substantially more positive influence on his team's RA/9 innings than any other catcher.  You begin to see differences in CERA only when a team employs multiple catchers that see significant playing time, ensure that none catch a majority of the innings.  This is exactly the type of small sample situation that should make you put LESS faith in the numbers, not more.

And we haven't even considered offense, where Posada holds a huge edge in OPS+ (130 to 49) versus Molina this year.  We all know that offense is FAR more quantifiable and measurable than game calling or pitch framing. 

Jorge Posada should start tonight's game.  Jose Molina barely belongs on a Major League roster.