There is a HUGE home field advantage in the NFL right now, but only on Sundays
This is by far my favorite time of the year to make NFL predictions! By this point in the season all the bye weeks are out of the way and there's plenty of data from the current season I can use to model future performance. The playoff picture is still in flux for many teams, and even if they're guaranteed a spot, there's still a question of seeding that gives teams something to play for down the road. It is also far enough along in the season that you really start to see many team's level of performance drop, which is especially true for teams that are playing away from home. And for the past three years, this dip in the visiting teams ability to score points seems to peak around this time in the season.
Given above in figure 1 is data on overall performance* for all teams over the course of the NFL season. The two lines represents the average of all teams performance for both home (red) and away (blue) games since the 2016-17 season, with the shaded areas representing the confidence of fit of these data. You can see that by week 13 (green line) that on average the home team scores about 1.5 points more than you would expect, while the visiting team scores around 3.5 points less than you would expect. This home advantage lasts until the end of the season, but this effect seems to be greatest at this time of year.
I broke down team performance by season in figure 2 just to see if there was one year that was bringing down the average of the others. The home effect appears to be in play for all previous seasons since 2016, with the trends for this year pointing again to a big advantage for the home team for week 13. When you look at this same performance metric for Thursday and Monday games (figure 3), there doesn't seem to be an advantage to being the home team for week 13. All three visiting teams won their games on Thursday this week, and the total of two out of the three games being under the betting line.
I have some ideas why the home team has such an advantage that I'll save for a later date, but right now I just want to get this out before today's games get going. There's some unusual weather for some of these games, so we'll see if the home team still does better than expected.
-Michael Edwards, Bioinfo Solutions LLC
*See previous blog post for an explanation on the performance metric
**Microsoft Excel for Mac ver.16.2 and JMP Pro ver.14 were used to collect, analyze and display all NFL data.