Interceptions and My Idiotic Perception

 The other night I was out with Jason and we were having a discussion about quarterbacks.  I made a comment about how I think defensive backs will eventually benefit from this new passing heavy league.  My idea was that if there more passes being thrown, then it should make sense that there will be more interceptions.  Jason argued with me and feels that it is a horrible time for defensive backs.

I figured (and I think towards the end of a very long rant that Jason agreed with me) that if QBs are throwing way more passes and the rate of interceptions stays relatively the same over time, that there should be more total interceptions.  My reasoning was that if you looked back at the old days, there were less passes thrown, but aside from a few outliers, interception numbers would probably be pretty low as well.

I was completely wrong.  I am actually shocked by what I found.  Here is the data:  INT is interceptions, the next column is interceptions per team per game, the next one is pass attempts, after that we have pass attempts per team per game, and last we have the percentage of passes thrown for interception (or interception per attempt).

Year	INT	INT/Tm/Gm	Pass Attempts	PA/Tm/Gm	Int/Attempt
2011	506	0.9882	17410	34.0039	2.9064%
2010	511	0.9980	17269	33.7285	2.9591%
2009	525	1.0254	17033	33.2676	3.0823%
2008	465	0.9082	16526	32.2773	2.8137%
2007	720	1.4063	17045	33.2910	4.2241%
2006	520	1.0156	16389	32.0098	3.1729%
2005	506	0.9883	16464	32.1563	3.0734%
2004	524	1.0234	16354	31.9414	3.2041%
2003	538	1.0508	16493	32.2129	3.2620%
2002	528	1.0313	17292	33.7734	3.0534%
2001	545	1.0988	16181	32.6230	3.3681%
2000	634	1.2782	16322	32.9073	3.8843%
1999	562	1.1331	16760	33.7903	3.3532%
1998	509	1.0604	15489	32.2688	3.2862%
1997	479	0.9979	15729	32.7688	3.0453%
1996	542	1.1292	15966	33.2625	3.3947%
1995	512	1.0667	16699	34.7896	3.0661%
1994	474	1.0580	15056	33.6071	3.1482%
1993	469	1.0469	14414	32.1741	3.2538%
1992	519	1.1585	13408	29.9286	3.8708%
1991	488	1.0893	13950	31.1384	3.4982%
1990	480	1.0714	13516	30.1696	3.5513%
1989	559	1.2478	14338	32.0045	3.8987%
1988	553	1.2344	14131	31.5424	3.9134%
1987	540	1.2054	13491	30.1138	4.0027%
1986	581	1.2969	14469	32.2969	4.0155%
1985	602	1.3438	14423	32.1942	4.1739%
1984	584	1.3036	14325	31.9754	4.0768%
1983	620	1.3839	14047	31.3549	4.4138%
1982	349	1.3849	7933	31.4802	4.3993%
1981	609	1.3594	14180	31.6518	4.2948%
1980	627	1.3996	13705	30.5915	4.5750%
1979	597	1.3326	12979	28.9710	4.5997%
1978	639	1.4263	11829	26.4040	5.4020%
1977	562	1.4337	9786	24.9643	5.7429%
1976	497	1.2679	10260	26.1735	4.8441%
1975	533	1.4643	9973	27.3984	5.3444%
1974	500	1.3736	9609	26.3984	5.2035%
1973	470	1.2912	8845	24.2995	5.3137%
1972	480	1.3187	9011	24.7555	5.3268%
1971	544	1.4945	9412	25.8571	5.7799%
1970	510	1.4011	9796	26.9121	5.2062%
1969	544	1.4945	10377	28.5082	5.2424%
1968	554	1.5220	10034	27.5659	5.5212%
1967	593	1.6943	10329	29.5114	5.7411%
1966	535	1.5923	10090	30.0298	5.3023%
1965	480	1.5584	9059	29.4123	5.2986%
1964	501	1.6266	9187	29.8279	5.4534%
1963	514	1.6688	8954	29.0714	5.7405%
1962	567	1.8409	8812	28.6104	6.4344%
1961	564	1.8312	8922	28.9675	6.3215%
1960	493	1.8396	7813	29.1530	6.3100%
1959	221	1.5347	3714	25.7917	5.9505%
1958	243	1.6874	3951	27.4375	6.1503%
1957	231	1.6042	3339	23.1875	6.9182%
1956	240	1.6667	3282	22.7917	7.3126%
1955	258	1.7917	3820	26.5278	6.7539%
1954	294	2.0417	4232	29.3889	6.9471%
1953	306	2.1250	4267	29.6319	7.1713%
1952	297	2.0625	4024	27.9444	7.3807%
1951	288	2.0000	3881	26.9514	7.4208%
1950	343	2.1987	4307	27.6090	7.9638%

I realize it looks like a lot to digest, so I was nice and made some graphs.

A few quick notes:  1982 was a shortened season, only nine games were played.  From 2011-2002 there were 32 teams that played 16 games.  From 2001-1999 there were 31 teams.  1998-1995 30 teams.  1994-1978 28 teams.  1977-1976 28 teams playing 14 games.  1975-1970 26 teams playing 14 games.  1969-1960 was the AFL-NFL times (I had to combine the numbers, the majority of the time they both played 14 games, except in 1960 when the NFL only played 12 games).  From 1959-1951 there were 12 teams playing 12 games and in 1950 there were 13 teams that played 12 games.

Here is the interesting thing, the number interceptions has stayed pretty steady since the 1960s.  In fact, as the number of attempts increases over time, the rate of interceptions decreases.  To me that seems pretty crazy, but I guess it should make sense if you take into consideration that coaches must know what they are doing.  I mean, if all these QBs were pretty crappy, they probably would want them to continuing throwing less.  Also, there are the rule changes to take into consideration.  I am not about to go that deep into this.

I am shocked that coaches passed at all in the 1950s, teams were averaging two interceptions per game and there was almost an 8% chance of an attempt being picked off.

I guess being a defensive back in this era must really suck.