Era-Adjusted TD/INT Ratios

by Chase Stuart on August 15, 2016

in Statgeekery

On Saturday, I asked the question: Is TD/INT Ratio Now Meaningless? That question was shorthand for a less hot-takey view, but fortunately I’m lucky enough to have smart readers who engaged in some excellent discussion in the comments. One of those guys, Bryan Frye, brought up the idea of a TD/INT+ Ratio, or an era-adjusted version.

I spent a bit of time playing with different ways to adjust for era, including using Z-Scores. One problem there was that the variance in TD and INT Rates is pretty significant from year to year, which makes the Z-Score heavily influenced more by year-to-year fluctuation that true era adjustments. So here’s what I did, using Milt Plum in 1960 and Tom Brady in 2010 as examples. Those two players rank 4th and 5th in this system despite playing 50 years apart. The raw numbers? Brady had a 9:1 TD/INT Ratio with 36 TDs and 4 INTs, while Plus was at 4.2:1, courtesy of 21 TDs and 5 INTs.

1) First, we convert to rates. Plum threw 250 passes, while Brady had almost exactly double, with 492 attempts. Plum averaged 8.40 TD/100Att, while Brady was at 7.32 TD/100Att. On the other hand, Plum was at 2.00 INT/100Att, vs. 0.81 INT/100Att for Brady.

2) Next, we adjust for era, using only players who had enough pass attempts to qualify for the league passing crown, and taking a simple average of the rates of those players. Therefore, for the 1960 NFL season, the TD/100Att average was 5.34, while the INT/100Att average was 7.13. So Plum was at 157% of league average at throwing touchdowns and 357% of league average at avoiding interceptions.

Brady? Well, in 2010, the qualifying passers averaged 4.47 touchdowns and 2.78 interceptions per 100 pass attempts. This means he was at 164% of league average in touchdowns and 342% at avoiding interceptions

3) Finally, we multiply the two rates. So Plum’s Adjusted TD Rate times his Adjusted INT Rate was 5.61, while Brady was at 5.60.

Here are the top 300 seasons by this measure. The best season came from yes, Damon Huard in 2006. Here’s how to read the table below. Playing with the Chiefs, Huard threw 11 TDs and just 1 INT in 2006, an 11.00 TD/INT Ratio (the 3rd best ever). He threw 244 attempts that year, and averaged 4.51 TDs per 100 pass attempts. The league average was 3.89, so Huard was at 116% of league average. He threw just 0.41 interceptions per 100 attempts, while the league average was 3.05. That gives him an INT+ of 745%. Multiply those two numbers — 116% and 745% — and you get a value of 8.63, which ranks as the best era-adjusted TD/INT rate of all time.

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Rk	QB	Team	Year	TD	INT	TD/INT	Att	TD/A	LgAvg	TD+	INT/A	LgAvg	INT+	VALUE
1	Damon Huard	KAN	2006	11	1	11.00	244	4.51	3.89	116%	0.41	3.05	745%	8.63
2	Nick Foles	PHI	2013	27	2	13.50	317	8.52	4.51	189%	0.63	2.67	423%	7.98
3	Josh McCown	CHI	2013	13	1	13.00	224	5.80	4.51	129%	0.45	2.67	597%	7.68
4	Milt Plum	CLE	1960	21	5	4.20	250	8.40	5.34	157%	2.00	7.13	357%	5.61
5	Tom Brady	NWE	2010	36	4	9.00	492	7.32	4.47	164%	0.81	2.78	342%	5.60
6	Aaron Rodgers	GNB	2011	45	6	7.50	502	8.96	4.31	208%	1.20	2.89	242%	5.03
7	Bart Starr	GNB	1966	14	3	4.67	251	5.58	4.69	119%	1.20	4.76	399%	4.74
8	Tom Brady	NWE	2007	50	8	6.25	578	8.65	4.18	207%	1.38	3.09	224%	4.63
9	David Garrard	JAX	2007	18	3	6.00	325	5.54	4.18	133%	0.92	3.09	335%	4.45
10	Steve DeBerg	KAN	1990	23	4	5.75	444	5.18	4.37	118%	0.90	3.34	370%	4.39
11	Roger Staubach	DAL	1971	15	4	3.75	211	7.11	4.52	157%	1.90	5.28	279%	4.38
12	Aaron Rodgers	GNB	2014	38	5	7.60	520	7.31	4.55	161%	0.96	2.50	260%	4.18
13	Steve Bartkowski	ATL	1983	22	5	4.40	432	5.09	4.56	112%	1.16	4.32	374%	4.17
14	Brian Griese	DEN	2000	19	4	4.75	336	5.65	4.09	138%	1.19	3.21	269%	3.72
15	Bart Starr	GNB	1964	15	4	3.75	272	5.51	5.09	108%	1.47	4.72	321%	3.48
16	Brett Favre	MIN	2009	33	7	4.71	531	6.21	4.23	147%	1.32	3.08	234%	3.43
17	Steve Young	SFO	1992	25	7	3.57	402	6.22	4.03	154%	1.74	3.75	215%	3.32
18	Peyton Manning	IND	2004	49	10	4.90	497	9.86	4.53	218%	2.01	3.02	150%	3.27
19	Peyton Manning	DEN	2013	55	10	5.50	659	8.35	4.51	185%	1.52	2.67	176%	3.25
20	Charlie Conerly	NYG	1959	14	4	3.50	194	7.22	5.60	129%	2.06	5.17	251%	3.23
21	Vinny Testaverde	NYJ	1998	29	7	4.14	421	6.89	4.23	163%	1.66	3.27	197%	3.20
22	Dan Marino	MIA	1983	20	6	3.33	296	6.76	4.56	148%	2.03	4.32	213%	3.16
23	Aaron Rodgers	GNB	2009	30	7	4.29	541	5.55	4.23	131%	1.29	3.08	238%	3.12
24	Ken O'Brien	NYJ	1985	25	8	3.13	488	5.12	4.20	122%	1.64	4.17	254%	3.10
25	Joe Montana	SFO	1989	26	8	3.25	386	6.74	4.10	164%	2.07	3.79	183%	3.00

Showing 1 to 25 of 300 entries

As always, please leave your thoughts in the comments.

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