After disovering that a single year of NFL football did not provide enough data for singnificant coefficients for things such as run defense, I expanded the database to include teams and games from the years 2003-2006, 4 years in total. Instead of 32 teams worth of data, I now have 128.
Let's begin at looking at our new data by examining the correlation of our offensive and defensive efficiency variables with season wins.
Correlation Coefficients, 5% critical value (two-tailed) = 0.1736 for n = 128
The correlation between wins and defensive run efficiency (DRUN) is found to be negative, which makes sense. The fewer yards allowed per rush, the more wins a team tends to have. But although the direction of effect is as expected, it is still not significant.
All other variables are significant however. Turnovers correlate the strongest, followed by offensive pass efficiency, then defensive passing efficiency. The running game just doesn't seem to be that important. For some reason offensive running ability appears to be more important than defensive running ability.
What does any of this mean? It is more evidence of how important turnovers are. They should not be discounted such as the Rams attempted under Martz. Secondly, the passing game is significantly more important than the running game on both sides of the ball. If I'm a general manager with a choice between a great pass rusher and a great run stopper, I'd take the the pass rusher. A choice between a receiver and running back--take the receiver, unless the running back is also a great pass blocker.
I think this means the death of the "smashmouth" football team. Running only appears to be important, because teams that are ahead (and very likely to win) run out the clock, racking up run yardage a losing team won't get. While total rushing yards appear to correlate well with winning, yards per rush attempt tells a very different story.
But shouldn't running out the clock count for something? It allows teams to hold onto leads, and it should therefore contribute to wins. You might think so, but the numbers say no. It just doesn't matter that much, or at all.
