Thursday, December 22, 2011

Betting Market Power Rankings – Week 16

by Michael Beuoy

Here are the week 16 betting market power rankings. I have provided two versions this time because I think the default methodology is breaking down this late in the season. The default methodology incorporates the following week’s spreads into the rankings, if they’re available. Because week 17 often includes meaningless games for teams trying to stay healthy for the playoffs, the spreads don’t necessarily reflect the true strength differential.

For example, the week 17 line for the Green Bay- Detroit game has Green Bay as a 3 point underdog. At home. It’s not very likely that the market thinks that Detroit is truly 5.5 points better than Green Bay, but it does appear to expect Green Bay to have things wrapped up by week 17 and not be playing at full strength.

So, I have provided two versions of the rankings. The first is the standard approach, which includes week 17 lines (probably not reliable). The second excludes week 17 from the rankings, and appears to make more sense.

The goal I had was to generate a set of point-based rankings that would best predict how the betting market would set the point spread for the coming week’s matchups. The better I was able to match the point spread, the better the rankings were a reflection of the market’s estimate of team by team strength. Through trial and error experimentation, I found that using point spreads for the most recent five weeks (with higher weighting given to more recent weeks), combined with an adjustment that accounted for actual game outcomes, generated the best predictive accuracy. More detail here.

Week 16 Rankings – Including Week 17 Lines (probably not reliable)

- The betting market rank as of the prior week (using the same methodology).
GPF - Stands for Generic Points Favored. It’s what you would expect a team to be favored by against a league average opponent at a neutral site.
GWP - Stands for Generic Win Probability. I converted the GPF into a generic win probability using the following formula: GWP = 1/(1+exp(-GPF/7)). This gives a more direct comparison to the ANS rankings.
ANS RNK - The Advanced NFL Stats Team Efficiency rankings for the same week.
ANS GWP - The Advanced NFL Stats Generic Win Probability for the same week.

1 NE28.00.7640.68
2 NO38.00.7530.68
3 BAL45.00.6890.61
4 GB15.00.6850.67
5 DET105.00.67100.57
6 ATL75.00.66120.56
7 SF64.50.66130.52
8 PHI124.50.6660.65
9 PIT54.50.6520.74
10 SD114.00.63110.57
11 DAL93.00.6070.63
12 NYJ83.00.60160.50
13 NYG131.50.5680.63
14 MIA180.50.52180.48
15 TEX140.00.5110.76
16 CIN17-0.50.49150.50
17 CAR23-0.50.49230.42
18 SEA20-0.50.48240.42
19 WAS24-0.50.48190.48
20 TEN16-1.00.46210.45
21 ARZ22-1.50.45220.43
22 DEN15-2.00.42250.39
23 RAI21-2.50.41140.52
24 MIN25-3.50.37320.28
25 CHI19-4.00.36170.48
26 BUF26-4.50.35200.45
27 KC30-5.00.32270.34
28 CLE27-5.50.32260.35
29 TB29-6.50.28300.30
30 JAC28-6.50.28280.34
31 IND32-7.50.25310.29
32 STL31-9.00.22290.32

Week 16 Rankings – Excluding Week 17 Lines

1 NE29.00.7940.68
2 GB18.50.7750.67
3 NO37.50.7430.68
4 SF65.00.68130.52
5 PIT55.00.6720.74
6 BAL45.00.6790.61
7 ATL74.50.65120.56
8 PHI124.50.6560.65
9 DAL93.50.6270.63
10 NYJ82.50.59160.50
11 SD112.50.59110.57
12 DET101.50.55100.57
13 NYG131.00.5480.63
14 MIA181.00.53180.48
15 SEA200.50.52240.42
16 TEX140.00.5110.76
17 CIN17-0.50.49150.50
18 WAS24-0.50.48190.48
19 CAR23-1.00.47230.42
20 DEN15-1.00.47250.39
21 TEN16-1.50.44210.45
22 ARZ22-2.00.43220.43
23 CHI19-2.50.42170.48
24 RAI21-3.00.39140.52
25 MIN25-4.50.35320.28
26 BUF26-4.50.35200.45
27 KC30-5.00.32270.34
28 CLE27-5.50.31260.35
29 TB29-6.50.28300.30
30 JAC28-7.00.27280.34
31 IND32-8.00.24310.29
32 STL31-8.50.23290.32

• There’s a new number one, with New England leap-frogging Green Bay for the top spot (but only ahead by a half point)
• Philadelphia was one of the bigger movers this week and is now ranked as the best team in the NFC East.
• The Lord taketh away – After moving up five spots last week from 20 to15, Denver drops back down to 20.
• The Colts were able to crawl out of both the Betting Market Ranking basement as well as the ANS Ranking basement. Yay?

Prediction of This Week’s Point Spreads
See below for how well the ranking methodology predicted this week’s point spreads. Note that the “PRED LINE” column excludes both week 17 lines (because it is unreliable) as well as week 16 (because I want to see how well the model does when it can’t “peek” at the answers)

GamePred LineActLineDiff
 ARZ @ CIN 4.54.0-0.5
 CHI @ GB 13.513.0-0.5
 DEN @ BUF 0.5-2.5-3.0
 JAC @ TEN 8.57.5-1.0
 MIA @ NE 11.59.5-2.0
 NYG @ NYJ 4.53.0-1.5
 PHI @ DAL 2.51.5-1.0
 SF @ SEA -2.5-2.50.0
 STL @ PIT 15.516.00.5
 TB @ CAR 8.57.5-1.0
 TEX @ IND -5.5-6.0-0.5

I probably won’t generate these rankings next week (I will be out of town without access to a computer and the rankings themselves probably won’t have much value, owing to the week 17 issue). However, I am thinking I may try to update these after each playoff week, as a way to see how the market continues to re-evaluate team strength.


SportsGuy said...

Those numbers don't look quite right in the last table.

Michael Beuoy said...

The rankings table or the line prediction table?

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