NFL QB Ratings 1940 - 2007

The graphical illustration above shows the league average QB Ratings by year, for every year from 1940 to 2007.  As you can see, there has been a steady increase over time, and the average continues to increase.  There are many reasons for this, of course, including the gradual importance and development of the passing game, the changing of the rules to favor the passing game, the introduction of the West Coast Offense, etc.  In the next graph, I'll show each of the components that contribute to this increase in the QB Rating.