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.