A not-quite-crisis of confidence

I still see plenty of opinions about the conventional wisdom that states that a good running game improves the passing game and vice versa, contradictory to what I observed in a couple months ago:

http://jasonwinter.blogspot.com/2009/06/can-brett-help-adrian.html
http://jasonwinter.blogspot.com/2009/06/brett-adrian-part-2.html
http://jasonwinter.blogspot.com/2009/06/you-cant-un-learn-things.html

Specifically (and against my better judgment), I've gotten into it a bit on a recent post on the Pro Football Reference blog. A commenter trotted out the following bits of wisdom:

1) You can't trust Tarvaris Jackson's numbers last year because of the small sample size; and
2) The Vikings' strong running game was responsible for Tarvaris Jackson's good numbers late in the season.

Note that that running game has been in effect for the last 32 regular season games and, by and large, Vikings quarterbacking has been mediocre to poor over that stretch, excepting the final four games of the 2008 season. So, T-Jack's numbers should be discounted due to a small sample size of games, but clearly the running game helps the team's quarterbacks -- which was only true for a small sample size of games. Eh?

But I'm not here to rag on a fellow commenter/blogger. Rather, I've been thinking about my theories the past few months and, while I still think they're mostly true, I can't help but shake some flaws with the analysis. They aren't necessarily deal-breakers, but they could show there's more to the interaction between running and passing than simple correlation.

As I've mentioned before, I'm no trained statistician or anything, just a football fan with a love of numbers and a willingness to challenge conventional wisdom. Maybe that'll get me in trouble someday, but until someone can come up with real, valid evidence to the contrary -- something more than "Well, it's obvious that a strong running game opens up the passing game, I mean, look at how much better quarterback X was when his team got running back Y!" which ignores all the times a quarterback doesn't improve when his running game improves -- I'll stick to my guns.

That said, here are some of the possibilities for why I might be wrong:

1) I'm looking at the wrong stats. Primarily, I use yards per carry and adjusted net yards per attempt, or an averaging stat for one (rushing or passing) versus a total yardage stat for the other (passing or rushing). Might be I'm comparing the wrong stats or, just as likely, I'm using the wrong tools to compare them.

2) Limitations on salary or coaching proficiency make it impossible to be great at both running and passing. Put simply, if you sink all your money into having a great running game -- a star back, big offensive linemen, a blocking tight end -- you're less likely to have anything left over to invest in quarterbacks and receivers. And some coaches might also just be better at engineering a great running game than passing game, or vice versa. This is the same concept that typically makes teams that are good on offense less likely to be equally good on defense, and it holds true for most major sports (hitting vs. pitching in baseball, offense vs. defense in basketball, etc.). My studies show that teams that run the ball well typically aren't exceptional at passing but maybe that's got less to do with there actually being a correlation from an in-game standpoint and more to do with the lack of ability (or funds) to construct a solid passing game.

3) Maybe there really is an effect, but it's undetectable. If you have the best running game in the league and the 20th best passing game, is it because there's no correlation between the two? Or is there a correlation and your passing game would be the 25th (or worse) best in the league without the strong running game? Using my Drew Brees-to-the-Vikings example, if Brees did take over at QB, maybe Adrian Peterson and Chester Taylor would have better years, but how would we separate Brees' effect on the running game from Peterson's, Taylor's, and the offensive line's normal development and improvement. I don't know.

I'd welcome anyone with strong analysis and the ability to use facts (instead of "conventional wisdom") to support or refute my arguments, because even I admit I feel a little tentative to expound my theories too loudly. But if you're going to disprove what I've written, at least try to be somewhat nice about it :)