CMI - 1940 to 2007

I thought I had posted this earlier.  It is a set of graphical illustrations of CMI from 1940 to 2007.  For comparison sake, I have included NFL average QB Rating in the 2nd graph.  CMI is defined as follows:

CMI = Completions/Attempts - 3 * Interceptions/Attempts

This ratio can never exceed 100.0% (although it can be negative).

In my mind, a running back has 2 duties once he receives the ball - run with it, and don't fumble it.  Similarly, a wide receiver has 2 duties once he receives (catches) the ball - run with it, and don't fumble it.  And, a quarterback, similarly has 2 duties - complete the pass, and don't turn it over.  I realize it's too simplistic a view.  Eventually, I will incorporate sacks and fumbles into the formula.  Since I am very interested in comparing quarterbacks over time, once sacks are included, I can only go back in time to 1969 (since sack data was included).