Determining Upset Magnatude
Originally, I was going to measure upset magnatude using the match-up ratio (the "ρ" value) originally published for the game. But after some (unposted) analysis, it seems clear that the match-up ratios are not comparable from week-to-week. They start out very high at the start of the season, and decline as it goes on.
So the first modification I made was to use the APR power index values from the second-to-last week of the season (I avoided the last week to rule out anomolous effects of teams resting their starters). However, the normal APR algorithm gives less weight to early season games.
Rather than try to justify why the week 2 Chargers @ Broncos game was one of the top-10 upsets of the season, I decided to use the unweighted version of APR power indexes, which gives all games played equal weight.
Determining the Top 10 Upsets
Using the unweighted APR power indexes for week 17, a list of all games where the predicted winner lost was compiled. This list was then sorted according to each game's match-up ratio (ρ).
Any loss that was (in my opinion) attributable to teams not playing all-out was eliminated from the list. The top 10 games from this list is presented below.
The Top 10 Upsets of the 2008 Season
As determined by the unweighted APR power indexes from week 16.
- Week 5: Buccaneers 13, Broncos 16 (ρ=1.1168)
From week 3 to week 15, APR had the Buccaneers ranked in the top 10. Maybe they just weren't ready to play at Mile High, but somehow the Buccaneers let the Broncos give them their second loss.
- Week 16: Jets 3, Seahawks 13 (ρ=1.1312)
Because the Jets couldn't put up two touchdowns on the Seahawks, they went from "win and you're in" to "win (and with help) you're in". The win and the help never came.
- Week 3: Jaguars 23, Colts 21 (ρ=1.1383)
The Jaguars won just 5 games this year, and this was one of them. It's hard to argue against Peyton Manning as MVP when a key loss like this is largely attributable to Manning's early season health problems.
- Week 7: Jets 13, Raiders 16 (ρ=1.1385)
Because the Jets couldn't put up two touchdowns on the Raiders... yeah, there seems to be a theme here. You might argue whether Jets @ Seahawks or Jets @ Raiders is the bigger upset, but they're both pretty bad.
- Week 11: Broncos 24, Falcons 20 (ρ=1.1398)
The Falcons had a chance at the #2 seed going into week 17. If they had won this game (their only home loss of the season), they would have had a much better chance.
- Week 12: Jets 34, Titans 13 (ρ=1.1398)
At the time, this didn't seem like that much of an upset. But that was (right) before the Jets went on a 1-4 skid, and finished out of the playoffs.
- Week 17: Raiders 31, Buccaneers 24 (ρ=1.2029)
Coming in to week 17, the Buccaneers still had a chance for the playoffs (and would've been in, had they won). All they had to do was beat the 4-11 Raiders. But there was no defense, no win, and no playoffs.
- Week 6: Rams 19, Redskins 17 (ρ=1.2192)
It says something about how bad the Rams were this year that this game is on this list in spite of the Redskins late-season troubles.
- Week 6: Giants 14, Browns 35 (ρ=1.2483)
Easily the low-point to the Giants season. Given the way the offense was struggling (Eli Manning threw 3 interceptions), the defense would've needed a masterful performance to keep them in the game. Instead, the Browns scored at will for much of the game.
- Week 7: Cowboys 14, Rams 34 (ρ=1.3023)
Brad Johnson will get his fair share of blame for this loss (the Cowboys didn't have a second drive for more than 21 yards until garbage time). But the defense was at fault, too: the Rams scored on their first 3 drives, and didn't punt for the second time until the 3rd quarter. If the Cowboys had won this game, they wouldn't have needed a win over the Eagles in week 17 to get in the playoffs.
Eliminated Games
The only game eliminated from the above list is the Titan's week 15 loss to the Texans (which would have been the #5 upset). At that point in the season, the Titans had already clinched the AFC South and a bye week, and only needed to beat the Steelers in week 16 to clinch the #1 seed in the playoffs. This was a meaningless game for the Titans.
