NFL Preseason to Regular season correlation

So, there have been a few posts over on MileHighReport talking about the team's preseason performance so far.  There's been some speculation that in recent years defensive stats have been a decent indicator of regular season performance.  I wanted to test this a bit, checking to see if there was any real link between the two.

Going back to 2012, I found total yards allowed per game in pre and regular season, as well as yards per play.  The results were not encouraging.  In the following chart, we'll see Yards per game has an R^2 of just .11, an extremely basic correlation.

 

Yards per play is even worse, with an R^2 of just .03.

We shouldn't expect there to be any real predictive power for preseason play.  Schemes offensively and defensively are vanilla through and through, with no game planning to attack weaknesses.  You also get extreme variance with a lot of guys playing extended snaps, who will likely be selling cars in a few weeks.