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Compu-Picks Analysis: Home Field

Mr Pac Ten
Posted Mar 29, 2011


2011 Compu-Picks Analysis Part 1: Home-Field Advantage Overview

As many of you know, home field advantage is a substantial part of compu-picks, both in terms of how it picks games and how it rates teams (those who have an unusually high number of home games take a ratings hit, and those with an unusually low number of home games get a ratings boost). Some people have questioned why it looks at home-field advantage at all, much less why it makes a material adjustment for it. The answer is simple: home-field advantage is REALLY important in college football.

Take a look at the following table, consisting of the W/L record of home teams in league play across 1-A football for the last six seasons (2005 - 2010):

Home W/L Record - League Games Only

All League Games Same League Record Home 1 Game Better Home 1 Game Worse
Total BCS 864 - 680 56.0% 124 - 66 65.3% 126 - 52 70.8% 85 - 99 46.2%
Total 1538 - 1233 55.5% 209 - 107 66.1% 231 - 81 74.0% 128 - 170 43.0%
Home 2+ Games Better Home 2+ Games Worse Records Within 1 Game Count: Within 1 game / Not
Total BCS 471 - 31 93.8% 58 - 432 11.8% 335 - 217 60.7% 552 / 992 35.8%
Total 870 - 62 93.3% 100 - 813 11.0% 568 - 358 61.3% 926 / 1845 33.4%

There are a few important takeaways from this table:

1) In even matchups, the home team wins 2/3 of the time
If you get nothing else away from this article, remember this statement. When two teams who end up with the same league record play each other, the home team wins just about 2/3 of the time (66.1%). If anyone doubts why home-field is a huge deal, that's the reason in a nutshell.

2) Traditional measurements of home-field advantage are artificially dampened
You probably also noticed that despite the huge edge in even matchups, the home team only wins league games at an overall rate of only 55.5%, which is the number (give or take) most likely to be cited when anyone talks about home field. The reason why that number is much lower is that most matchups aren't close. When Alabama plays Vandy, it doesn't matter whether it's in Tuscaloosa or Nashville, because Bama is going to win anyway. And while most league games aren't matchups to that extreme, few are close matchups, much less genuine tossups.

As the table shows, in only 1/3 of all league games (33.4%) do the two teams finish within one win of each other in the league standings. And if the two teams aren't within one game of each other, you can pretty confidently pick the better team to win, regardless of location.

But when it isn't a mismatch, home-field advantage comes into play much more strongly. 66.1% when they finish with the same record, 61.3% when the teams are within a game of each other. That's a huge winning rate for games that are supposed to be close.

3) Home teams score major upsets much more often than road teams
A road team that finishes 2+ games worse than its opponent hits the upset 6.7% of the time, but 11.0% of the time if they're at home. Even though the difference between the win percentages is only 4.3%, considering how infrequently these upsets happen, that's still a huge difference.

4) Home-field advantage does NOT substantially vary between BCS and non-BCS leagues.
Everyone knows that home-field advantage is bigger in the big schools. And everyone is wrong. It's actually virtually identical between the BCS leagues and everyone else.

Interestingly, there IS (or at least has been) substantial variation between individual leagues. I'll go into that more later on.

There are also a few more minor takeaways / points of interest.

5) The Big 12, Big East, Mountain West and C-USA have especially strong home-field advantages.
The below table expands the first one, showing six-year home records by league:

Home W/L Record - League Games Only

League All League Games Same League Record Home 1 Game Better Home 1 Game Worse
ACC 164 - 125 56.7% 26 - 12 68.4% 28 - 7 80.0% 17 - 30 36.2%
Big 12 163 - 113 59.1% 22 - 11 66.7% 24 - 5 82.8% 18 - 8 69.2%
Big East 97 - 71 57.7% 20 - 5 80.0% 9 - 6 60.0% 9 - 11 45.0%
Big Ten 143 - 120 54.4% 20 - 15 57.1% 22 - 9 71.0% 11 - 17 39.3%
Pac-10 147 - 118 55.5% 12 - 13 48.0% 18 - 11 62.1% 20 - 12 62.5%
SEC 150 - 133 53.0% 24 - 10 70.6% 25 - 14 64.1% 10 - 21 32.3%
Indep 2 - 5 28.6% 1 - 1 50.0% 0 - 0 0 - 2 0.0%
Mountain West 127 - 89 58.8% 13 - 3 81.3% 23 - 4 85.2% 9 - 11 45.0%
C-USA 168 - 120 58.3% 17 - 11 60.7% 24 - 7 77.4% 16 - 14 53.3%
MAC 158 - 154 50.6% 20 - 13 60.6% 22 - 7 75.9% 9 - 23 28.1%
Sun Belt 98 - 90 52.1% 15 - 10 60.0% 17 - 9 65.4% 7 - 11 38.9%
WAC 121 - 95 56.0% 19 - 3 86.4% 19 - 2 90.5% 2 - 10 16.7%
Total BCS 864 - 680 56.0% 124 - 66 65.3% 126 - 52 70.8% 85 - 99 46.2%
Total 1538 - 1233 55.5% 209 - 107 66.1% 231 - 81 74.0% 128 - 170 43.0%
League Home 2+ Games Better Home 2+ Games Worse Records Within 1 Game Count: Within 1 game / Not
ACC 79 - 10 88.8% 14 - 66 17.5% 71 - 49 59.2% 120 / 169 41.5%
Big 12 88 - 6 93.6% 11 - 83 11.7% 64 - 24 72.7% 88 / 188 31.9%
Big East 52 - 2 96.3% 7 - 47 13.0% 38 - 22 63.3% 60 / 108 35.7%
Big Ten 81 - 2 97.6% 9 - 77 10.5% 53 - 41 56.4% 94 / 169 35.7%
Pac-10 85 - 5 94.4% 12 - 77 13.5% 50 - 36 58.1% 86 / 179 32.5%
SEC 86 - 6 93.5% 5 - 82 5.7% 59 - 45 56.7% 104 / 179 36.7%
Indep 1 - 0 100.0% 0 - 2 0.0% 1 - 3 25.0% 4 / 3 57.1%
Mountain West 78 - 1 98.7% 4 - 70 5.4% 45 - 18 71.4% 63 / 153 29.2%
C-USA 93 - 9 91.2% 18 - 79 18.6% 57 - 32 64.0% 89 / 199 30.9%
MAC 95 - 14 87.2% 12 - 97 11.0% 51 - 43 54.3% 94 / 218 30.1%
Sun Belt 54 - 6 90.0% 5 - 54 8.5% 39 - 30 56.5% 69 / 119 36.7%
WAC 78 - 1 98.7% 3 - 79 3.7% 40 - 15 72.7% 55 / 161 25.5%
Total BCS 471 - 31 93.8% 58 - 432 11.8% 335 - 217 60.7% 552 / 992 35.8%
Total 870 - 62 93.3% 100 - 813 11.0% 568 - 358 61.3% 926 / 1845 33.4%

Focusing on the "All League Games" and "Records Within 1 Game" sections, these four leagues stand out as having especially strong home-field edges, both overall and in close matchups (I'll get to the WAC later). The Big 12 is especially striking, with the home winning at well over 60% when the records are the same, when the home team is one game better, AND when the home team is one game WORSE in the final standings.

The Mountain West has home teams winning at a similarly impressive clip, over 70% when the final league records are within a game of each other, and just shy of 59% overall. Even more striking is the fact that they did this despite having a very substantial record disparity, with less than 30% of all league matchups being "close" (final record within 1 game). CUSA and the Big East didn't have quite as striking numbers, but they were still solidly above-average.

Interestingly, the WAC had home teams winning at almost a 73% clip when the records were close, but only at a 56% rate overall. I could be mistaken, but it looks like the reason for this is that in the WAC, only 25.5% of all league games were close, far below average and in fact the lowest number anywhere. This suggests that the "true" HFA in the WAC is being dampened by the fact that the bulk majority of the games are simply mismatches. But that's just a guess on my end.

6) The SEC, MAC and Sun Belt have had especially weak home-field advantages.
It's been said in a few places that the SEC has lower home winning rates than other leagues, and the data bears this out (though it's worth noting that the SEC had one of the highest home winning rates in 2010, so it MAY be changing). For whatever reason, the SEC has had an especially high home winning rate in even matchups, but especially low across the rest of the board, most notably most notably for big home underdogs, who pulled off upsets at only half the national rate.

The MAC is especially striking, as the home winning rate is barely above 50%, and the home win rate is below average almost across the board.

I'm actually very curious if any of my readers has a good explanation why the Big 12, Big East, MWC and CUSA have such strong home-field advantages, and why the SEC, MAC and Sun Belt have such weak ones. I'm playing with the theory that distance is a big driver (longer distance = bigger HFA), since the SEC, MAC and Sun Belt cover relatively small geographic footprints, while the aforementioned four cover relatively large ones (this theory would also suggest that the WAC should have an especially large home-field advantage, given how widely spread out it is, which agrees with the idea that its HFA is dampened by the wide talent disparity).

Another reasonable guess is that weather/environment plays a factor, since the SEC, MAC and Sun Belt have similar weather patterns, and lack extreme altitude programs like Colorado (Big 12) or the majority of the Mountain West. Meanwhile the Big 12 is half Texas/Oklahoma and half freezing, the Big East runs from New England to Florida (with Syracuse playing in a dome), and the Mountain West has warm weather TCU, UNM and SD St, with the rest cold weather (though I don't think CUSA fits into this theory very well).

Some technical notes and caveats:

1) This article only looked at intra-league games.
I chose to look only at league games because inter-league games introduce a whole slew of biases, from the fact that better teams usually make favorable scheduling arrangements to the fact that some leagues are much better than others to the fact that every team schedules differently, which means that you can't just analyze teams by their simply W/L record.

By choosing to only look at league play and league records, I avoided these issues. In every league, there is long-term parity between home games and road games (though some teams will have one more home game this year and one more road game the next), and in every league the schedules are determined by the league and tend to be reasonably equal.

There's still the issue of division strength (a 4-4 Big 12 South team tends to be better than a 5-3 Big 12 North team, for instance), as well (slightly) unbalanced home-road splits in a given year, but overall, it should be a pretty consistently good measurement of quality.

Of course, it's reasonably possible that by only looking at league games I've missed important information. I may take a look at the non-league games sometime later this offseason and see if I can come up with anything interesting.

2) I've used 2010 league alignments for all seasons.
Other than WKU joining 1-A, I don't recall there being any realignment moves from 2005 - 2010. It's possible I may have overlooked something, though if I have it shouldn't be material to the high-level points.

3) League title game wins were counted as league wins.
This throws a little bit of noise into the numbers, but I don't think it's at all material. If someone wants to run the numbers adjusting for this and prove me wrong, go for it.

2010 Compu-Picks Blog

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