For more than 50 years, the National Football League has struggled with the problem of how to rate passers statistically. Passing champions have been crowned in nine different ways, as follows:
1932-37: Most yards gained passing.
1938-40: Completion percentage.
1941-48: Best record in six categories--total completions, completion percentage, total yards, touchdowns, interceptions, interception percentage.
1949: Same as 1941-48 but minus interception percentage.
1950-59: Average gain per pass attempt.
1960-61: Best record in six categories--total completions, completion percentage, total yards, total touchdowns, average gain, interception percentage.
1962-71: Best record in four categories--completion percentage, interception percentage, total touchdowns, average gain.
1972: Same as 1962-71 except that total touchdowns changed to touchdown percentage.
1973 to present: Same categories as 1972 with a new scoring system. It used to be that 1970 passers, for instance, could only be measured against other 1970 passers. Now they can also be measured against a perfection standard. This enables 1970 passers to be compared with 1945 or 1985 passers.