What percentage of teams win based on the Vegas point spread?

Question: What percentage of teams win based on the Vegas point spread?

Why I asked the Question: I entered my first NFL survivor pool this year and wanted to know at what point spreads do the chances increase for guessing the correct winner between two teams.

Analysis: I did an online search trying to find the past lines with little luck. There are a ton websites on gambling and after going through a few hundred, I found the following that had the lines:

http://www.footballlocks.com/nfl_point_spreads.shtml

- NFL lines for 2006 and 2007 (towards bottom of page):

http://www.collegefootballpoll.com/weekly_picks.html

- College lines back to the 2003 season.

Even though I was not looking for the college number, I decided to run the numbers anyway. I did want more data for the NFL , especially since they have about 200 less games with point spreads than college games do (in 2007 there were 677 college games with lines vice 353 NFL games). I then noticed that Phil Steele's Pro Football publication had the lines back to 2003. I asked them where they got there numbers and they gave me the following website which has NFL and college lines back to 2001:

http://www.ncsports.com/online/schedulepage.html

A combo of the two databases could be used, but Vegas and the people betting on the games seemed to be less accurate guessing college games (probably for less information available), so the two were kept separate.

Games with ½ point spreads had less games than the other games around them, so I also created a weighted percentage. It is 50% from that specific line, 16 % for each ½ point away and 9% for each 1 point away. This helps with evening out impacts a huge upset in the extreme values. For example Stanford's 24-23 upset of USC when they were a 39.5 point underdog. There were much more lines at even numbers vice ½ so this help to smooth the winning percentages from one value to the next.

Note: The college games from 2005 don't have ½ point lines.

So far I have complete comparisons on NFL 2004 to 2007 and college 2005 to 2007 and here is the results. I will add data as I find time to go back through the previous years..

NFL – Vegas's line's year by year winning percentage:

2007 69.6%

2006 59.6%

2005 75.1%

2004 64.1%

Total 67.1%

College - Vegas's line's year by year winning percentage:

2007 73.7%

2006 75.4%

2005 72.3%

Total 73.8%

Percent chance for a team to win the game base on point spread (using the weighted values)

Percentage	NFL	College
100	15	41
95+	14	21.5
90+	14	16.5
85+	11.5	16
80+	8	14
75+	8	13.5
70+	7	6.5
65+	5	5.5
60+	3.5	5
55+	1	2
50+	--	1
45+	--	--

Complete NFL list (2004 to 2007)

Vegas Spread	Total wins	Total losses	Winning Percent	Weighted (50%,34,16%)	Percentage break points
24.5	1	0	100	100
22	1	0	100	100
20	1	0	100	100
19	1	0	100	100
18	1	0	100	100
16.5	4	0	100	100
16	2	0	100	100
15.5	3	0	100	100
15	4	0	100	100	100%
14.5	3	0	100	98.77
14	2	0	100	95.67	90%-95%
13.5	11	2	84.62	87.78
13	11	3	78.57	83.45
12.5	8	1	88.89	85.74
12	5	1	83.33	84.34
11.5	7	1	87.5	85.63	85%
11	12	3	80	82.42
10.5	14	2	87.5	84.35
10	21	7	75	80.3
9.5	29	3	90.63	85.26
9	26	8	76.47	81.94
8.5	9	1	90	85.09
8	21	3	87.5	81.94	75%-80%
7.5	18	11	62.07	71.5
7	49	14	77.78	72.44	70%
6.5	31	17	64.58	67.08
6	37	22	62.71	66.72
5.5	26	9	74.29	69.31
5	18	8	69.23	67.37	65%
4.5	16	12	57.14	62.96
4	31	15	67.39	64.39
3.5	62	33	65.26	62.17	60%
3	107	90	54.31	57.91
2.5	23	20	53.49	56.47
2	22	12	64.71	59.28
1.5	16	14	53.33	55.78
1	26	21	55.32	55.73	55%
	679	333

Complete College list (2005 to 2007)

Vegas Spread	Total wins	Total losses	Winning Percent	Weighted (50%,34,16%)	Percentage break points
46	1	0	100	100
45	1	0	100	100
44	1	0	100	100
43	1	0	100	100
42	2	0	100	100
41	1	0	100	100	100%
40.5	1	0	100	96
40	2	0	100	91.5
39.5	1	1	50	75
39	4	0	100	91.5
38.5	2	0	100	96
38	2	0	100	97.33
37.5	1	0	100	93.19
37	2	1	66.67	80.9
36	6	1	85.71	87.19
35	4	0	100	94.9
34.5	2	0	100	98.86
34	8	0	100	100
33.5	1	0	100	100
33	4	0	100	100
32.5	1	0	100	100
32	6	0	100	100
31.5	3	0	100	100
31	9	0	100	100
30.5	1	0	100	100
30	10	0	100	99
29.5	2	0	100	96.28
29	7	1	87.5	90.35
28.5	4	1	80	87.88
28	14	0	100	94.93
27.5	5	0	100	96.98
27	11	1	91.67	95.83
26.5	2	0	100	98.58
26	20	0	100	98.61
25.5	4	0	100	98.45
25	10	1	90.91	95.45
24.5	6	0	100	98.45
24	14	0	100	98.83
23.5	4	0	100	99.06
23	17	1	94.44	97.22
22.5	4	0	100	99.06
22	18	0	100	99.1
21.5	5	0	100	98.03	95%
21	33	2	94.29	94.08
20.5	7	1	87.5	89.18
20	30	4	88.24	86.9
19.5	4	1	80	84.38
19	22	4	84.62	87.71
18.5	5	0	100	94.35
18	30	1	96.77	94.79
17.5	16	2	88.89	92.88
17	47	3	94	93.22
16.5	15	0	100	92.61	90%
16	35	9	79.55	83.87	85%
15.5	9	3	75	79.84
15	29	5	85.29	81.95
14.5	15	4	78.95	80.58
14	55	10	84.62	81.69	80%
13.5	21	6	77.78	76.97	75%
13	37	13	74	73.93
12.5	6	4	60	70.23
12	48	9	84.21	80.17
11.5	8	1	88.89	84.2
11	41	7	85.42	82.75
10.5	13	4	76.47	77.3
10	37	20	64.91	71.76
9.5	8	2	80	75.62
9	44	16	73.33	73.85
8.5	9	3	75	75.07
8	43	18	70.49	73.17
7.5	21	4	84	77.44
7	61	36	62.89	70.71
6.5	33	6	84.62	75.71	70%
6	54	33	62.07	67.1
5.5	17	8	68	66.54	65%
5	49	28	63.64	62.51	60%
4.5	11	9	55	58.44
4	50	33	60.24	58.49
3.5	25	20	55.56	56.65
3	65	51	56.03	56.84
2.5	30	21	58.82	57.07
2	53	40	56.99	55.79	55%
1.5	11	11	50	52.87
1	55	47	53.92	53.5
	1426	507