Note: Due to some technical difficulties on the Patriots Daily site, we're running Outside Foxborough on FO this week.
A significant portion of the talk surrounding this week's upcoming Jets-Patriots game has revolved around the betting line for the game, and how dramatic it is in light of both the Patriots' historic offensive attack and a perceived desire for retribution following the Week 1 "Cameragate" incident.
For those of you unfamiliar with a betting line, allow me to provide you with an example.
DALLAS (-7.0) (-$120)
WASHINGTON (+7.0) (+$105)
In this example, Dallas is the home game, as their team name is capitalized. They are favored by seven points over Washington. These seven points constitute what is known as "the spread". What that means is simple: For a bet on Dallas to be successful, Dallas must beat Washington by more than seven points in order for them to "cover" the spread. If Dallas wins by exactly seven points, the bet is a push and the bettor's money is returned. For a bet on Washington to be successful, they need to win, tie, or lose by less than seven points.
The second part of the line, to the right, contains what you'll need to gamble to make $100 on your bet. In Dallas' case, the negative sign in front of the $120 indicates that the odds are such that a casino will pay you $100 if you gamble $120 on Dallas, which would return a total of $220 to the bettor. In Washington's case, the positive sign means that if you bet $100 on Washington, you'll receive $105 in winnings, for a total of $205 in return. In short, if the sign is negative, it refers to how much you'll need to gamble to win $100; if it's positive, it refers to how much you can win for gambling $100.
Now that the explanations are out of the way, let's take a look at the Jets-Patriots line. In this game, the spread has been at or around 24 points all week. That's right at the accepted record for history's largest line, which was a 1976 encounter between the Pittsburgh Steelers and the Tampa Bay Buccaneers, who were an expansion team. The Steelers won, 42-0, and covered. If the line gets to 24.5, it would be a new record.
What all that in the hopper, can we make any sort of prediction about whether the Patriots are likely to cover this gargantuan line? Of course, that's where the data comes in.
Intrepid FO intern Matt Accornero went and found the betting lines in all games that occurred from 2001 through 2006. For many, he found both the opening and closing lines, although some opening lines are missing. This provides us with 1594 games to analyze, which isn't an irrefutable sample, but is certainly a sample that should reveal some trends, if there are any. For the purposes of this study, we'll be looking at the closing lines.
Of course, where the sample becomes a larger issue at the margins, which is where we are with the Patriots this year. Simply put, not many teams get to go into games with a 20+ point margin; in fact, not a single team in our dataset had a 20+ point spread. The closest were the 2002 Eagles, who played the Texans at home giving -19.5 points, in a game where they did not cover, only beating the Texans by 18.
First, I checked to see whether the lines change depending upon the time of the season -- namely, does Vegas feel more confident about teams later in the year, and respond to that by setting more robust lines?
| Avg Spread | Avg Outcome | Diff | |
| Weeks 1-4 | 2.32 | 2.56 | 0.24 |
| Weeks 5-8 | 2.41 | 3.21 | 0.80 |
| Weeks 9-12 | 2.45 | 1.61 | -0.84 |
| Weeks 13-17 | 2.67 | 2.59 | -0.08 |
In that table, the Avg. Spread being 2.32 means that the home team was favored, on average, by 2.32 points. (All spreads in the article are relative to the home team.) They won by 2.56 points, or .24 points more than the expectations of the line. As you can see, the line does rise slightly as the season goes along, but not so much to be a significant difference. Furthermore, the average outcome doesn't seem to be particularly affected, so it's hard to say that familiarity really affects the spread.
Next, of course, I wanted to see if there were any trends that existed in teams beating the spread. First, I checked point differentials in games and compared them to the pre-game spreads, to see if there were any differences. I marked games where the difference between the expected outcome (the spread) and the outcome itself was more than three points. I also ignored spreads that didn't have at least ten games of results to draw from.
| Line | Diff |
| -7.5 | 3.9 |
| -7 | 0.9 |
| -6.5 | 0.6 |
| -6 | -1.0 |
| -5.5 | -2.6 |
| -5 | |
| -4.5 | -5.5 |
| -4 | -1.7 |
| -3.5 | 1.9 |
| -3 | -0.9 |
| -2.5 | 1.8 |
| -2 | -3.1 |
| -1.5 | 1.1 |
| -1 | 3.1 |
| 0 | 1.1 |
| 1 | -4.7 |
| 1.5 | 0.2 |
| 2 | 0.5 |
| 2.5 | -2.0 |
| 3 | -0.6 |
| 3.5 | 2.8 |
| 4 | 0.1 |
| 4.5 | 0.9 |
| 5 | 1.9 |
| 5.5 | 0.3 |
| 6 | -0.5 |
| 6.5 | 0.3 |
| 7 | 0.7 |
| 7.5 | 3.5 |
| 8 | 0.9 |
| 8.5 | -0.7 |
| 9 | -2.3 |
| 9.5 | 2.6 |
| 10 | 1.8 |
| 10.5 | -0.9 |
| 11 | -2.1 |
| 11.5 | 3.9 |
| 12 | -5.1 |
| 12.5 | |
| 13 | -0.4 |
| 13.5 | -6.2 |
When the line of a game was -7.5 points, or in other words, when the road team in a game was favored by 7.5 points, the average score saw the road team win by 3.6 points, or the home team lose by 3.6. That results in a difference of +3.9 points from the expected margin.
As you can see, the ends of the spectrum saw much more dramatic differences from the expected scoreline than the middle. Unfortunately, it doesn't mean much, because the differences were strewn in opposite directions. Take a look at the 11.5 and 12-point spreads; in games where the spread saw the home team favored by 11.5 points, the home team won, on average, by 15.4 points; in games where the spread was 12 points, the home team only won by 6.9 points. In other words, there's no real indicator of what a big line does beyond the fact that it's more likely to see variance than a small spread.
A natural followup: Are favored teams more likely to cover in certain types of games than others?
| Spread | Favorite | Underdog |
| -7.5 | 25% | 75% |
| -7 | 35% | 56% |
| -6.5 | 33% | 67% |
| -6 | 50% | 50% |
| -5.5 | 65% | 35% |
| -5 | 56% | 33% |
| -4.5 | 70% | 30% |
| -4 | 50% | 46% |
| -3.5 | 41% | 59% |
| -3 | 46% | 46% |
| -2.5 | 49% | 51% |
| -2 | 60% | 33% |
| -1.5 | 46% | 54% |
| -1 | 43% | 57% |
| 0 | 55% | 45% |
| 1 | 42% | 58% |
| 1.5 | 53% | 47% |
| 2 | 55% | 45% |
| 2.5 | 39% | 61% |
| 3 | 43% | 48% |
| 3.5 | 58% | 42% |
| 4 | 45% | 53% |
| 4.5 | 51% | 49% |
| 5 | 59% | 41% |
| 5.5 | 53% | 48% |
| 6 | 45% | 53% |
| 6.5 | 50% | 50% |
| 7 | 49% | 49% |
| 7.5 | 58% | 42% |
| 8 | 44% | 52% |
| 8.5 | 50% | 50% |
| 9 | 39% | 61% |
| 9.5 | 54% | 46% |
| 10 | 50% | 42% |
| 10.5 | 43% | 57% |
| 11 | 31% | 69% |
| 11.5 | 57% | 43% |
| 12 | 40% | 60% |
| 12.5 | 38% | 63% |
| 13 | 46% | 54% |
| Avg. | 48% | 51% |
Basically, no. The only thing that's even remotely worth noticing and looks the slightest bit consistent is that heavy road favorites (here, -6.5 to -7.5 points for the home team) aren't likely to cover. Of course, the Patriots have been favored by way more than 7.5 points on the road at points this year.
What about that magical item in our bag of holding known as DVOA? Well, it may be able to offer us some assistance. The difference between two teams' seasonal DVOA has a very strong (+.54) correlation with the difference in points between them in that game. The difference between the Jets and the Patriots' DVOA, through thirteen games, is 79.7% -- large, but not the largest in our dataset. If we note the scores of all games with a difference of 75% more between the overall DVOA of the two competitors, the average margin of victory in said games is…23.7 points. Not bad.
Finally, is DVOA smarter than Vegas? Well, realistically, no. If it was, Vegas would have snatched us up, and you wouldn't be reading this column. Is it helpful? Sure. There are 34 games in which the line of the game was six points or more, while there was a difference in DVOA of ten percentage points or more in the other direction. For example, when Green Bay took on Detroit in Week 3 of the 2006 season, Green Bay (2006 season DVOA: -1.4%) was a 6.5 point underdog heading to Ford Field, whose Lions' 2006 DVOA was -19.5%. The result? A seven-point Packers win, which would be a credit to DVOA as opposed to the Vegas line. In those 34 games, DVOA went 23-11. In all fairness, the DVOA metric we're looking at has a whole season's results in it, while Vegas can only see what's been played so far. If we only look at games played in Week 9 and later, though, DVOA remains successful (8-6) against the spread.
Unfortunately, our look into the numbers didn't reveal too much into being able to make an informed decision about whether to bet on the Patriots or the Jets on Sunday. I'm personally inclined to take the Jets for several reasons, primarily because of their pacing. The Jets have been one of the slowest teams in the league over the past few years, using a slow, ball-control offense while playing defense against teams that gashed them on the ground, using up more plays and time in the process. Furthermore, while we haven't done the research into this topic, I would imagine the swirling winds and blustery weather predicted limiting both teams some offensively. All in all, I obviously would predict a Patriots victory, but it might only end up being by a couple of scores instead of four or five.