SSS: Testing for a real Home Field Advantage

So as I continue doing research for my course,  I decided to jump into the vast database at http://www.pro-football-reference.com  and answer a very simple question:

Is there convincing evidence that the Denver Broncos have an advantage when playing at their home stadium, Invesco Sports Authority Field at Mile High?  (p.s. … Why can’t they just call it Mile High Stadium?
You can access the data file here.

Bottom Line?  Yup:

They won 63% of their games at home and 46.5% of their games on the road.

Could this have happened by chance?  Again , I ran a simulation in Fathom to help answer my question. How did the simulation turn out?

1000 simulations of 199 games, where no home field advantage exists. We recorded difference in home and away win rates over 199 games. a 16.5 percentage point advantage for the home team doesn't occur very often by luck.

1000 simulations of 199 games, where no home field advantage exists. We recorded difference in home and away win rates, and plotted what actually happened at Invesco Field from 2001-2012. A 16.5 percentage point advantage for the home team doesn’t occur very often by luck.

This difference is unlikely to occur by luck if there is no real home field advantage (<2% of the time could the Broncos have been so lucky without a real home field Advantage).

Next question:  What about Mile High Stadium (the original stadium)? How does the advantage at Invesco compare to the one at Mile High?  

Before 2001, when Denver was at the Original Mile High Stadium, Denver’s home-filed win rate was 202/320 = 0.637.   Their away-field rate was 124/314 = 0.394.  This difference of 23.7 percentage points seems HUGE.  How likely could such a big difference happen by chance with if home-field advantage doesn’t exist?

The difference in win rates between home and away games (.631-.394 = .236) is plotted against what might happen by chance over 634 games  if no home field advantage exists.

The difference in win rates between home and away games (.631-.394 = .236) is plotted against what might happen by chance over 634 games if no home field advantage exists.

Yeah: There’s CLEAR evidence that there was a home-field advantage at Mile High stadium as well.

About roughlynormal

I have been a math/statistics teacher for 20 years. I currently teach at a college prep school in southern California. I also coach teaching fellows for Math for America - Los Angeles chapter. I love my career, my colleagues, and my friends & family.
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