Last week, I posted some quick numbers on the new stadiums from 1997-2003, and the winning percentage of the road team based on the number of visits they previously made to that new stadium. Commenter "Guy" had a concern about team quality:

Don't you need to account for the strength of these 12 teams, and the visiting teams? These twelve teams, in their 2nd, 3rd, and 4th seasons in the new stadiums (when many of the first-time visits must have occured), were a combined .564 overall. If you assume a HFA of 70 points, we'd expect them to be about .634 at home -- not that much lower than you found. If the first-time visitors happened to be slightly below average (which they likely were, since these 12 home teams are above average), that could account for the remaining gap.

As a quick correction, I need to point out that there were actually thirteen teams in my study, but I forgot to list the Houston Texans and Reliant Stadium, though they were included in the data set. But I'm sure Guy would have the same question even knowing the Texans were part of the data set, and rightly so. When I first began looking at this several months ago and then stored it away for a rainy day, I did not have "against the spread" records readily available. However, we do have "against the spread" data for all the games in question, so I figured I would dig back in and try to account for team strength.

By using "against the spread" numbers, we should have some built in control for team quality, at least the public perception of the at-the-moment strength of the two teams. The spread numbers also have home field advantage, at least the generic home field advantage, built in to them. Thus, we can see whether the factor of visiting a stadium for the first time is there, once we account for team strength and normal home field advantage. Let's get to the numbers presented from the perspective of the visiting team, based on number of prior visits to the stadium.

The first time visitors were 1.3 points worse than the spread on average. That 0.453 "against the spread" winning percentage in games for road teams in their first visit is statistically significant (p=0.03) compared to the expected .500 record "against the spread". Those numbers listed above do not include the 2009 results for the thirteen stadiums used in the study. So far this year, road teams in their first visits to those stadiums are 2-6-1 against the spread, underperforming the spread by 9.1 points.

Here's a list of those 2009 games:

What about when we separate out the first visit by the year in which it occurred?

Nothing conclusive here about the effect weakening over time. It makes sense that there might be some general institutional knowledge (from players changing teams, etc.) that gets passed around the league over time, but this doesn't show that during what is basically the first 8 years of a stadium's existence.

Finally, I thought I would go back and look at the first year, with the against the spread data, and look at the records based on the order of the visitors in the first season. I didn't include Arizona and Indianapolis in the original data set because few teams have played multiple times in those two stadiums. However, as I am only looking at first year performance here, I added them in to this one. This lists the against the spread record of the visitor based on when that game was played in the first season. The Game 9 row includes all playoff games played in the new stadiums in the first season. While we only have 15 cases for each game, the results are in line with what I would expect as the home team gained greater comfort with the new stadium over the course of the first season.