Graphing Vegas' Opinion

For the last few weeks I've been comparing the spreads for the top teams to their Pomeroy projections in an attempt to gauge the oddsmakers' opinions of various teams. Today I thought I'd take a look at the progression of a few top teams as the year went on; using the current Pomeroy projections of each team's entire regular season schedule and comparing them to the spreads of each game.

The Pomeroy projections provide a baseline to compare it to, to put each opponent on an equal playing field; UNC is obviously going to be favored by fewer points in ACC play than in November, so this baseline corrects for that. Doing this we can see if their spreads were significantly higher or lower than their projections at any point in the season, and how things have changed throughout the course of the year. This will make more sense once you actually see the graph, so here are the aforementioned Tar Heels:

North Carolina
Preseason AP rank: 1
Current rank: 2

The light blue line is the spread for each game minus the current Pomeroy prediction for that game. So, for example, in UNC's first game of the year they were favored by 32.5 against Penn; Pomeroy has them winning that game by 37.2. In the particular game, the oddsmakers were about five points lower on UNC. 

The dark blue line uses a moving average of the five most recent games to provide a more useful comparison; that can be seen as a snapshot of the oddsmakers' opinion of the team at that point in time, compared to their current Pomeroy rating. In this graph it looks like Vegas' opinion of the Tar Heels peaked about one-third of the way through the year, and they've been lowering their expectations ever since, to the point that they're currently right in line with their Pomeroy rating.

This is about what I expected for UNC. Some of their lines at the beginning of the year were absurd; that big spike in the individual games line is from when they were favored by 36 against Oral Roberts. Until recently, Vegas had them about three points above their current Pomeroy level. But, as you can see, over their last five games Vegas hasn't been as bullish on them. They were only favored by 9.5 at Virginia Tech; Pomeroy has them winning that game by 10.8. We'll have to wait and see what their lines are like during the ACC tournament, but right now it appears that no adjustment to their Pomeroy rating needs to be made.

Memphis
Preseason AP rank: 13
Current rank: 5

Vegas hasn't quite caught up to Pomeroy's lofty opinion of the Tigers, but the discrepancy is getting smaller and smaller. That big downward drop in the middle of the graph is from when Memphis played at Tennessee in late January; the Vols were favored by three, even though Pomeroy currently has Memphis winning that game by 6.6. A good deal of that gap can be explained by Tennessee's disappointing performance since, but their opinion of the Tigers has also increased dramatically over the last six weeks.

Missouri
Preseason AP rank: NR
Current rank: 15

Excluding that first game against Chattanooga -- they were favored by just 13.5, when KPom currently has them winning by 29.1 -- Mizzou's rise hasn't been as dramatic as I would've expected. It looks like they're risen by about three points in the oddsmakers' eyes since late November, while they've climbed from anonymity to the top tier of the Big 12. That may be because Vegas was significantly higher than the general public on Missouri before the year began, or realized they were going to be pretty good early on.

Oklahoma
Preseason AP rank: 12
Current rank: 4

There are some wild swings here at the beginning of the season -- that'll happen, as we've learned a lot more about teams like Davidson and Utah over the last few months -- but things level off around the time conference play starts. Even while the Sooners were breezing through the first 11 games of their Big 12 schedule, the oddsmakers didn't really change their opinion of them. And right now they seem to agree with Pomeroy that there are around 15 teams that are better than the projected #1 seed.

UCLA
Preseason AP rank: 4
Current rank: 20

This is another one that's kind of a mess in November and December; Texas and DePaul ended up being a lot worse than we thought they'd be. But, as with Oklahoma, the swings are a lot smaller beginning in January. The general public's opinion of the Bruins had decreased significantly over the course of Pac-10 play, but if anything the oddsmakers are now higher on them.