As I watched the Game of the Century last week and saw LSU beat Alabama, I asked myself, why was Alabama favored by 4.5 when conventional wisdom states that home field advantage is worth only 3 points, and Alabama was facing the #1 team in the country? They should not be favored by more than 3!

Could bookies be over-weighting the value of Alabama’s homefield advantage? Turns out they did, as LSU won the game by 3.

I double-checked Jeff Saragin‘s estimate of home field advantage, and it turns out it was lower than the expected 3 points, at 2.6. I wondered, is the value of home field advantage declining?

Yes, the value of home field advantage is on the decline.

Leveraging Jeff Saragin’s online models going back through the 1998 season, I charted the value of home field advantage in each season, and did a simple linear regression to determine the trend. Indeed, there’s a downward slope, and the R-squared is .47, not too shabby.

Why is this happening? Looking at the chart, it appears 2005 was the year things changed, with every year but 1 since then having home field advantage below 3 points.

Instant Replay was introduced in 2005!

Consistent with Sports Illustrated’s examination of what drives the value of home field advantage (officiating) (don’t have the link, here’s a similar piece published by Wired), the introduction of instant replay in 2005 drastically reduced the value of home field advantage. Here’s a chart with the averages pre and post-2005.

Up until 2005, home field advantage was worth almost 4 points. Once the impact of bad calls were reduced, which are more likely to be in the home team’s favor, home field advantage dropped precipitously to 2.6.

I don’t know if everyone’s expectations have been re-set on home field advantage, but don’t put as much stock in the home team. And, it Instant Replay technology improves, or the rules committee expands the uses or frequency of Instant Replay, expect the value of home field advantage to decline even further.

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