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Statistically Speaking: Steady as She Goes

Friday, June 09, 2006

Steady as She Goes


In keeping with the spirit of my previous post about consistency, I decided to conduct a little study to see which aspects of a college football team's performance are more consistent over time. Executing the study was simple, I simply calculated how many points per game each Division IA team scored in 2004 and determined how well they predicted each team's points per game in 2005 by using the r squared (correlation coefficient). Here's a technical definition. In laymen's terms, the r squared is the percentage of variation in the 2005 numbers that are explained by the 2004 numbers. I then did the same thing with each Division IA team's defense. The results are below, and to me they are a bit surprsing.

Correlation of points per game 2004-2005: .3375

Correlation of points allowed per game 2004-2005: .4108

Defense, at least from 2004-2005, is more consistent than offensive perfromance. This seems counter-intuitive because defense is a game of reactions. The offense dictates not only the pace, but also the personnel that the defense must have on the field. Later on this week, I will post the correlation for 2003-2004 and also 2002-2003 if I have time. If this holds true, it could be good news for teams like Georgia Tech and Alabama that have had good defenses for a few years running, but have been derailed by below-average offenses. Additionally, it could be bad news for teams like Notre Dame that had dramatic offensive improvements in 2005, but had similar defensive results. Of course, this data is at the macro level, and it would be prudent to consider each case individually when attempting to prospect how each team will do in 2006 relative to their 2005 numbers (graduating players, change in coaching style, etc.). As always, your thoughts on this seemingly counter-intuitive phenomenon are welcome.

1 Comments:

Anonymous Anonymous said...

Maybe this could be explained by saying that it's harder for an individual to have a huge impact on a defense than on an offense. Can any player change a defense's performance the way a QB can for an offense? That way predict that a defense has more continuity from one year to the next.

1:33 PM  

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