In this week's Varsity Numbers, Bill Connelly revisits some measures and concepts: Adjusted Scores, Covariance, and momentum (or whatever you choose to call it).
15 Apr 2009
by Bill Connelly
As spring football culminates with school-color-versus-other-school-color games throughout April, this seems like a pretty good time to revisit some 2008 statistics, put one final stamp on the season, and in coming weeks, start looking toward 2009.
The inaugural season of Varsity Numbers saw quite a few numbers and concepts thrown against the wall. Some did not stick, but one that did was the "+" concept, explored here in its introductory form and here with 2008 conference numbers.
Here's a quick refresher on the "+" approach:
[T]he "+" concept [is] a primitive attempt at a college-level look at DVOA-type comparisons discussed here. The formulas behind the "+" concept have been strengthened since the writing of that column (instead of looking at game totals and comparing them to opponents' per-game averages, it actually looks at per-play totals, eliminating the general per-game problem of small sample sizes), but the idea remains the same: Figure out a way to factor a team's strength of schedule into statistics to truly find the best offense, defense, and possibly overall team. You read "+" ratings the same way you would read OPS+ or something similar in baseball: 100 is exactly average, under 100 is bad, and over 100 is good.
(If you want to look at this as a DVOA figure of sorts, just subtract 100 and view it as a percentage. So a "+" figure of 122 could also be viewed as +22%. A "+" figure of 90 would be -10%. The Overall "+" figure below is the same way, only the base is 200 instead of 100.)
The "+" formula has been tweaked to include the strength of schedule of a team's opponents (there is now a component of a team's performance, a team's opponents' performance, and a team's opponents' opponents' performance, not unlike the RPI in college basketball), so you now get a truer read of how a team performed versus how an average team could have been expected to perform. In future weeks, we can break these stats down into more focused categories (non-passing downs vs passing downs, et al.), but we will keep it simple at first.
One other thing to remember about the "+" Rankings below: Stats are derived only from plays taking place in "close-game" scenarios, defined previously as follows:
So without further adieu, here are the final 2008 "+" rankings. Teams are ranked by combining their close-game offensive and defensive S&P+ ratings.
|2008 Final "+" Rankings|
|Rank||Team||Record||Off. S&P+ (Rank)||Def. S&P+ (Rank)||Total S&P+||Final AP Rank|
|1||USC||12-1||146.3 (3)||141.7 (3)||288.0||3|
|2||Florida||13-1||152.1 (1)||135.1 (4)||287.2||1|
|3||Oklahoma||12-2||151.7 (2)||129.3 (7)||280.9||5|
|4||TCU||11-2||103.5 (52)||170.3 (1)||273.8||7|
|5||Texas||12-1||124.6 (10)||146.4 (2)||270.9||4|
|6||Penn State||11-2||145.7 (4)||120.5 (15)||266.2||8|
|7||Boise State||12-1||120.5 (15)||133.0 (5)||253.4||11|
|8||Ohio State||10-3||120.5 (16)||132.3 (6)||252.7||9|
|9||Alabama||12-2||126.6 (9)||123.5 (8)||250.1||6|
|10||Missouri||10-4||124.4 (11)||116.7 (20)||241.1||19|
|11||Oregon||10-3||127.9 (8)||112.5 (29)||240.4||10|
|12||Georgia||10-3||135.4 (5)||102.5 (57)||237.9||13|
|13||Iowa||9-4||115.3 (25)||122.2 (11)||237.5||20|
|14||Oklahoma State||9-4||123.5 (13)||113.2 (27)||236.7||16|
|15||Texas Tech||11-2||128.0 (7)||105.7 (45)||233.7||12|
|16||Utah||13-0||116.7 (22)||116.5 (21)||233.1||2|
|17||Oregon State||9-4||115.1 (26)||117.7 (19)||232.8||18|
|18||Mississippi||9-4||122.8 (14)||109.6 (36)||232.4||14|
|19||Cincinnati||11-3||110.7 (34)||120.7 (14)||231.4||17|
|20||Kansas||8-5||118.1 (19)||111.9 (30)||230.2||--|
|21||Nebraska||9-4||119.9 (18)||108.9 (41)||228.8||--|
|22||Pittsburgh||9-4||110.3 (38)||117.9 (16)||228.3||--|
|23||South Florida||8-5||117.4 (21)||109.1 (38)||226.5||--|
|24||LSU||8-5||116.4 (23)||109.7 (35)||226.1||--|
|25||Illinois||5-7||112.8 (31)||111.8 (31)||224.6||--|
Only one team in the S&P+ top nine was not in the AP's final top ten, but there is still plenty of variation, especially after the first nine names. Let's look at some of the oddities.
Illinois: First things first: There was a team with a losing record in the S&P+ top 25, and it wasn't a team from the SEC or Big 12. How does this happen? Primarily it happens because of turnovers and poor special teams, both of which severely prohibited Illinois from making another serious run at the Rose Bowl. They were -6 in turnover margin (No. 89 in the country), plus they were No. 113 in net punting and No. 94 in punt returns.
[Why weren't turnovers factored into the "+" number formula (beyond just having a point value of zero where applicable)? Because turnovers are, to an extent, arbitrary. Interceptions are somewhat predictable and within a team's control, but fumbles bounce wherever they bounce, and sometimes a team just gets lucky and recovers more of them. Teams that benefit greatly one year from turnover margin tend to regress in the category the next year (case in point: despite little turnover in personnel, Missouri went from +13 in 2007 to -4 in 2008), so leaving turnovers mostly out of the S&P equation A) keeps things simple, and B) gives you a solid idea of who may be getting a bit lucky or unlucky.]
The final scores of eight of their 12 games were within two possessions, and Illinois went 2-6 in those games. They lost to No. 6 Penn State by 14 (it was 24-17 heading into the fourth quarter). They lost to No. 8 Ohio State by 10. They lost to No. 10 Missouri by 10. They were close to being a really good team, but they could not put it together. There are a number of potential reasons for this, but their down-to-down performance shows they could be dangerous in 2009.
Virginia Tech: You will not find Virginia Tech on the above list because the Orange Bowl champions finished No. 41 in S&P+ rankings. They were the anti-Illinois -- average performance (No. 79 offense, No. 22 defense, not a ton of credit given for shutting down a series of average ACC offenses), but a great turnover margin (+14). That, plus a "Beamer Ball" special teams unit, was good enough to get them to the ACC title game. It helped, too, that then-freshman running back Darren Evans surged down the stretch of the season (last six games: 157 carries, 778 yards), and the Hokies won four of their final five conference games (including the conference title game) to make the Orange Bowl.
Kansas: How does one become the highest-ranked five-loss team in the country? By beating the No. 10 team while losing to the No. 3, No. 5, No. 15, No. 21 and No. 23 teams. As much as their schedule helped them in their 11-0 start to the 2007 season, it killed them last year, and it will probably be the biggest obstacle between the Jayhawks and their first Big 12 North title in 2009.
Missouri: While we're at it, how does a four-loss Missouri team slip into the Top 10? In much the same fashion, actually. They lost to No. 3 and No. 5, and their other losses were statistically-even, last-second heartbreaks to the No. 14 and No. 20 teams. They also destroyed No. 21 Nebraska, which helped. Otherwise, as mentioned above, turnovers were not their friend, and that cost them dearly in the two tight losses.
TCU: How does a two-loss Mountain West team finish in the top four? By losing on the road to the No. 3 team (while holding them to their lowest regular-season point total), and losing to Utah in a statistically even road game (while giving up only 13 points to a good offense). They had by far the No. 1 defense in the country -- their 170.3 Defensive S&P+ was as close to No. 2 Texas' as No. 2 Texas' was to No. 10 Tennessee's. They held seven teams to single digits. Meanwhile...
Utah: The Utes went undefeated by winning five games by a possession or less and posting a +13 turnover margin. Utah was good, and while the Utes were better in the one statistic that mattered most when they played TCU -- the scoreboard -- the Horned Frogs were overall better statistically.
Tennessee, No. 32: Phil Fulmer's last Vol squad had one of the biggest ranges of rankings. They had the No. 102 passing offense and the No. 3 rushing defense. Overall their defense ranked No. 10, but their No. 80 offense very predictably held them back. They were the second-highest ranked team with a losing record.
Tulsa, No. 48. The Golden Hurricanes went 12-2, but their ridiculously weak schedule held them back. That, and a weak defense (No. 86). They sure had a fun offense (No. 20), though.
Wisconsin, No. 64: The S&P+ formula may have overrated Illinois, but that wasn't the case with the Badgers, who surprisingly came in with the No. 108 defense (No. 103 rushing, No. 102 passing). Not very Wisconsin-like.
West Virginia, No. 75: No ranking comes more surprising than this. Their No. 27 offense was balanced by their No. 116 defense (No. 114 rushing, No. 110 passing). We'll just say that West Virginia is to the "+" ranking what North Carolina was to the FEI last year -- a somewhat inexplicable outlier.
Washington State, No. 118: Interesting only because they're the lowest-ranked major-conference team, ranked higher than only No. 119 Idaho and No. 120 Western Kentucky.
This will be fodder for a future column, but for now we'll take a quick look at the major differences between the "+" ranking system and Brian Fremeau's FEI system.
West Virginia: The differences between FEI's No. 19 ranking of the Mountaineers and the No. 75 of the "+" could be the basis for its own entire column.
WAC Teams: The "+" likes the WAC a lot more than does FEI. Whereas the FEI had Hawaii ranked No. 108, Nevada No. 81 and Fresno State No. 83, the "+" rankings had them at No. 53, No. 36 and No. 61 respectively, differences of 55, 45 and 22 spots. In all, WAC teams averaged a ranking of 18 spots higher in the "+."
Big 12 Teams: The "+" also liked the Big 12 more, giving those teams an average ranking of 15 spots higher. Kansas was No. 20 (as opposed to No. 60 in FEI), Nebraska No. 21 (No. 59 FEI), Baylor No. 40 (FEI No. 75), Oklahoma State No. 14 (FEI No. 36) and Missouri No. 10 (FEI No. 29).
ACC Teams: On the flipside, the FEI was much, much higher on the ACC. North Carolina ranked only No. 46 in the "+" rankings, as opposed to No. 6 in the FEI rankings. Additionally, Miami (No. 67 vs No. 31), Georgia Tech (No. 49 vs No. 14), N.C. State (No. 62 vs No. 28), Virginia Tech (No. 41 vs No. 9), Duke (No. 83 vs No. 52), Florida State (No. 37 vs No. 10), Wake Forest (No. 39 vs No. 15) and Boston College (No. 35 vs No. 11) were all significantly different. In all, ACC teams averaged an FEI ranking 26 spots higher.
MAC Teams: The MAC was the mid-major version of the ACC, coming in much more favorably with the FEI (an average of 17 spots). Northern Illinois (No. 100 vs No. 61), Western Michigan (No. 106 vs No. 74), Temple (No. 95 vs No. 63) and Buffalo (No. 81 vs No. 51) had the highest variations.
The "+" rankings also ranked Big Ten teams an average of 10 spots higher, while the FEI slightly favored Big East and Conference USA teams (an average of five spots higher each).
What is the cause for this? The obvious answer is likely special teams to a small extent (the "+" rankings do not much account for that yet), the differences in measurement methods ("+" rankings look at play-level data, FEI at possessions) to a larger extent, and to an even larger extent the difference in means of calculating strength of schedule adjustments.
In the next offseason Varsity Numbers, we will begin to take a look at unit rankings and other interesting tidbits that could signify encouraging news for some teams and signs of foreboding for others.
23 comments, Last at 28 May 2009, 5:58pm by pokes