December 02, 2014


So I found some useful statistics to help in the development of a points-based quarterback assessment metric - call it Interception-Adjusted Points per Attempt, or IAPPA.

It's easy enough to see how many point a quarterback helped the team score - Aaron Rogers has thrown for 32 touchdowns this season.  Since the extra point is automatic nowadays, that gives us 32x7=224 points.

Now, what should we subtract for each interception?  Well, according to these tables compiled by Football Outsiders, the average NFL drive (2014 ytd) yields about two points - so when you throw an interception to the other team, you are giving them an incremental +2 to their normal expected scoring.

So: Aaron has thrown three interceptions this year, so we would (counts on fingers) subtract six points, giving him a IAP of 218...dividing by attempts (380) gives him an IAPPA of 0.57.  All clear?

Looking at the other end of the reality spectrum, Gino Smith of the New York Jets has thrown seven touchdowns, for 49 points, in 258 attempts.  His 11 interceptions, however, would get him a penalty of 22, leaving him with a IAPPA of (49-22)/258 = 0.10.  I'm pretty sure that's not good.

Here's the League (minimum 100 attempts):

Player Team IAPPG
Aaron Rodgers GB  0.57
Peyton Manning DEN  0.49
Andrew Luck IND  0.44
Tony Romo DAL  0.43
Tom Brady NE  0.41
Philip Rivers SD  0.38
Ryan Fitzpatrick HOU  0.36
Ben Roethlisberger PIT  0.35
Drew Brees NO  0.34
Carson Palmer ARI  0.32
Jay Cutler CHI  0.31
Joe Flacco BAL  0.31
Eli Manning NYG  0.30
Ryan Tannehill MIA  0.29
Mike Glennon TB  0.29
Russell Wilson SEA  0.28
Kyle Orton BUF  0.28
Matt Ryan ATL  0.27
Alex Smith KC  0.27
Kirk Cousins WAS  0.25
Mark Sanchez PHI  0.25
Colin Kaepernick SF  0.24
Austin Davis STL  0.23
Nick Foles PHI  0.23
Cam Newton CAR  0.19
Matthew Stafford DET  0.18
Andy Dalton CIN  0.18
Derek Carr OAK  0.17
Drew Stanton ARI  0.17
Teddy Bridgewater MIN  0.15
Josh McCown TB  0.15
Brian Hoyer CLE  0.14
Geno Smith NYJ  0.10
Blake Bortles JAC  0.10

To some degree we are rounding up the usual suspects - Rodgers and Manning look great of course, Smith and Bortles are in the basement again.  Wilson and Kaepernick look like twins, as they do on IAYPA.

But there are also some interesting differences.  Some players - like Hoyer - look good on IAYPA, but terrible here.  Tony Romo, who has never looked good on IAYPA, looks like a superstar in this system.  Andrew Luck usually looks middle-of-the-pack on IAYPA, but is elite here.

So, since points and yards are theoretically equivalent, and since the two systems yield somewhat different results, you can get a more robust take on quarterback efficiency by looking at both.  I suppose the next step is an IAYPA/IAPPA scattegram or cross table.  More on that story as it develops.


Blogger Laird of Madrona said...

Sorry, I'm not following you: do touchdowns matter, now?

December 3, 2014 at 12:23 AM  
Blogger The Other Front said...

I am considering the possibility that jointly considering yards and points would improve our assessment over considering one or the other alone.

So wtf do we do with Field Goals?

December 3, 2014 at 5:16 PM  

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