One of the things you could aways count on, along with death and taxes, was that dome teams and teams from warm weather locations would struggle in the cold of January in the NFL playoffs. Remember the Colts getting trounced 41-0 in the Meadowlands when Peyton Manning was younger? Or the Vikings going to the same venue in the NFC Championship Game against the Giants as a favorite only to lose by the same ridiculous scoreline? The Raiders getting crushed 51-3 in Buffalo in January 1991 also rates up there.
But it’s fair to wonder, as we head into a Championship weekend where the domed Vikings head to Philly, and the Jacksonville Jaguars go into Foxboro, whether the wintry advantage is becoming more muted. Last week, we saw the Jaguars go into Pittsburgh and jump out to a lead, while the Falcons did come up losers in Philadelphia. But enough of selected examples, let’s go to the full data.
Here are the records for all playoff games where the home team was from the Midwest/Northeast or Denver, and played outdoors, and the visitor was a team from Southern California, Arizona, Texas, or Florida–or a dome team.
If you look at just winning percentage, then the last decade hasn’t been much different than previous times. The home team in cold vs warm/dome matchups has won 76% of games over the last decade, identical with the 76% from 1978 to 2007.
But digging deeper, we see quite the difference. The against-the-spread record in the last decade is a still profitable 58% if you take the home team. It was an incredible 67% over the previous three decades, against a much larger sample size.
And then, there are the margins of covering. The average result in the last decade has seen the home team win by 9.1 points when the average point spread was 7.1, a 2 point difference. For the previous thirty years, the average was the home team winning by 11.4 points, even though the average point spread was smaller, resulting in the home team outperforming the spread by 5.4 points.
To make sure that this wasn’t a case of the betting markets getting smarter, I used the simple rating system rating of each playoff team. It turns out that the average point spread was 3.0 points above where it would have been predicted on a neutral field. That’s identical to the 3.0 points above predicted line on a neutral field from 1988-2007 (for some reason, the favorites were not favored heavily enough in the 1980’s, regardless of weather, and SRS predicted the lines should have been higher). So we haven’t seen a sudden shift in the home team being given a boosted home field advantage by the betting markets to offset the cold effects.
Now, we are dealing with only 17 games in the last decade, before the two this weekend, so it’s too early to say if this is a blip or a trend. (Since 2012, the 14 games show an even smaller 0.8 point difference between point spread and margin of victory.) But if it’s something that teams are getting better to deal with, it is possible that improvements in travel and increased knowledge on acclimatization could play a role. You can’t get rid of the advantage of a home team being better used to the cold, but perhaps you can reduce it.