IAPPA

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.