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Does Last Season Matter in College Football?

By Dr. Ed Feng 4 Comments

Plot of Yards Allowed Per Play in College Football

From 2010 to 2011, the correlation coefficient in yards per play allowed by defense was 0.496.

Numbers, especially those spit out of a computer, must pass the stupid test. If you think the results are stupid, then the numbers don’t pass the test.

After four weeks of college football, I was working on rankings that only included games from this year. Here at The Power Rank, we take football statistics like yards per play and adjust them for strength of schedule. But when I looked at the results for defense, Texas Tech had the top ranked defense.

Texas Tech?

The same defense that gave up 39.25 points a game last year, 117th in the nation?

Last year’s Texas Tech defense actually looked better by yards per play, ending the season ranked 75th in our defense rankings. (In the rest of this article, offense and defense rankings refer our calculations that adjust yards per play for strength of schedule.) But head coach Tommy Tuberville just brought in his 3rd defensive coordinator in 3 years. Even with a load of talent, a jump from 75th to 1st is almost impossible.

It doesn’t pass the stupid test.

How to Make The Rankings Better

We use past data to calculate rankings that predict the future. This depends on using variables that correlate from the past to the future. For example, yards per play allowed by a defense in the first 6 games of the season has a correlation coefficient of 0.481 with yards per play the rest of the season. In contrast, fumble recovery rates for a defense have almost no correlation between the first 6 games and the rest of the season. Hence, we look at yards per play but not fumble recovery rates.

But what about last season? Surprisingly, yards allowed per play correlates season to season with a coefficient of 0.496, even larger than the early to late season correlation. We also looked at other statistics, such as points per game and pass yards per attempt, both on offense in defense. In general, the season to season correlations were slightly smaller than the early to late season correlations.

But what’s going on behind these correlations?

During the season, yards per play is affected by injuries and the inherent randomness of football, such as that tipped pass that falls into a receiver’s hands for a long touchdown. Changing the yards gained on a play from 0 to 92 will have a dramatic effect on the game average. These factors make the early to late season correlation coefficient much less than 1.

From season to season, teams can have large turnover in players and coaches. I thought this would lead to a much smaller correlation coefficient. It doesn’t. One reason is the identity of the program. Texas has a huge fan base, lots of money, and a long tradition of recruiting stellar athletes from the Lone Star state. Rice has none of those things.

No perfect rankings early in the season

The strong season to season correlations suggests using last year’s results in this year’s rankings. In fact, we have been doing that so far, using all games last year and counting this year’s games twice. We will continue to do this.

But there are still problems.

For example, Baylor is still the top ranked offense. Given that the Bears lost quarterback Robert Griffin III to the NFL draft, this ranking is most likely too high. However, head coach Art Briles has led successful offenses at both Houston and Baylor. Moreover, senior quarterback Nick Florence has already led the Bears to 7.26 yards per play this year, much higher than the 5.45 average over all FBS and FCS games last season. With only this year’s games, Baylor is the 34th ranked offense due to weak competition. They will probably end the season somewhere in between 1st and 34th.

Last Season Does Matter in College Football

Surprisingly, key football statistics like yards per play correlates from year to year almost as strongly as it does from early to late season. While that certainly affects what games we use in our rankings, it also matters to fans. Reputation, tradition and money matter in college football. These factors don’t change overnight. Consider these 3 programs.

  • Michigan. The Wolverines had 3 horrible years under coach Rich Rodriguez. But in the 23 years before that, Michigan ended each season in the top 25 of our rankings. In the first year of this streak, a guy named Jim Harbaugh started his first game at quarterback. So it shouldn’t be too surprising that Michigan got back to 12th last year under new head coach Brady Hoke.
  • Auburn. The Tigers have almost 2 million fans and pack over 85,000 of them in Jordan-Hare Stadium for home games. Despite the ups and downs of this past decade, Auburn has never finished in the bottom of half of Bowl subdivision teams in our rankings. They won’t fall that low season either, although that won’t make Auburn fans happy with head coach Gene Chizik.
  • Rice. This small private school in Texas, which happens to be my alma mater, just isn’t a very good football program. The Owls have never finished in the top half of teams this decade, not even during their 10-3 season in 2008. Don’t expect much from this program.

Programs don’t change overnight. Keep that in mind as the season progresses.

Filed Under: Auburn Tigers, College Football, College Football Analytics, Football Analytics, Gene Chizik, Michigan Wolverines, Rice Owls

College Football Predictions, October 8, 2011

By Dr. Ed Feng 1 Comment

Oklahoma (6) will beat Texas (37) by 15.9 at a neutral site. Texas has a 0.18 chance of beating Oklahoma. Here we go again, trying to peer into the magic ball and forecasting the strength of this Texas team. While we were doubtful a few weeks ago after their win over UCLA, Texas thumped Iowa State 37-14 on the road last week. However, Texas had a +3 turnover margin and blocked a punt for a touchdown. As for Oklahoma, the last time they played a quality opponent the defense allowed Missouri quarterback James Franklin to throw for 8.8 yards per attempt while running back Henry Josey racked up 9.5 yards per carry, including a 48 yard touchdown run. So there’s an opportunity for the Texas offense to shine against what seems like a tough defense. In our rankings that only include games from this year, Oklahoma is favored by 9.3 over Texas at a neutral site, not much different from the 10.5 point line that favors Oklahoma.

LSU (5) will beat Florida (25) by 17.1 at home. Florida has a 0.17 chance of beating LSU. On the first play from scrimmage against Alabama, Florida quarterback John Brantley threw a 65 yard touchdown pass. The Gators gained 165 yards the rest of the game, including a rushing attack that had 0.5 yards per carry (29 total). Florida’s offensive performance against LSU will be an interesting measuring stick between the two of the best defenses in the country. Last year, LSU and coach Les Miles needed a perfect bounce on a fake field goal to sustain a game winning drive and pull out a 33-29 win at Florida. Moreover, LSU is probably a bit overrated in the rankings due to large turnover margins in their games against Oregon and West Virginia. So the line which favors LSU by 13.5 is probably pretty accurate, if not too high. Florida has a 0.22 chance of pulling the upset in Baton Rouge.

Auburn (8) will beat Arkansas (10) by 1.0 on the road. Arkansas has a 0.48 chance of beating Auburn. Our early season rankings that use a one year window of games probably doesn’t truly reflect this Auburn team. Using only games this year, Auburn is ranked 31st with a 6.42 rating instead of 8th with a 17.92 rating. The former is probably more accurate, although Auburn’s defense seemed to wake up last weekend in their win at South Carolina. The rankings with only this year’s games predicts Arkansas by 12.0, which implies Auburn has a 0.25 chance of pulling the upset.

Rice (113) will beat Memphis (120) by 16.7 at home. Memphis has a 0.17 chance of beating Rice. The line favors Rice at home by 20.5? This line says more about the weakness of Memphis (4 touchdowns worse than the average team) that any kind of strength for Rice (2 touchdowns worse than the average team). Here’s hoping that the algorithm is wrong and my alma mater covers.

Nebraska (17) will beat Ohio State (22) by 4.8 at home. Ohio State has a 0.39 chance of beating Nebraska. Ohio State is becoming a case study in what can happen to a team when it loses a top notch coach. Over the last 6 years, Jim Tressel never led Ohio State to a final season rating lower than 13.7. A 13.7 rating this year would put them at 11th. Instead, Ohio State is 59th with a -0.45 rating using only games this year. Their offense was difficult to watch in the 4th quarter against Michigan State last weekend. Nebraska is predicted to win by more than 10.0 by the line and our rankings that only use games this year.

Boise State (1) will beat Fresno State (80) by 25.5 on the road. Fresno State has a 0.08 chance of beating Boise State.

Alabama (3) will beat Vanderbilt (85) by 31.0 at home. Vanderbilt has a 0.05 chance of beating Alabama.

Stanford (4) will beat Colorado (83) by 29.7 at home. Colorado has a 0.06 chance of beating Stanford.

Oregon (7) will beat California (38) by 17.8 at home. California has a 0.16 chance of beating Oregon. Check out our preview.

Oklahoma State (9) will beat Kansas (98) by 31.1 at home. Kansas has a 0.05 chance of beating Oklahoma State.

Texas A&M (11) will beat Texas Tech (40) by 6.3 on the road. Texas Tech has a 0.36 chance of beating Texas A&M.

TCU (12) will beat San Diego State (45) by 7.0 on the road. San Diego State has a 0.34 chance of beating TCU.

Clemson (13) will beat Boston College (73) by 19.1 at home. Boston College has a 0.14 chance of beating Clemson.

Missouri (14) will beat Kansas State (49) by 6.8 on the road. Kansas State has a 0.35 chance of beating Missouri.

South Carolina (15) will beat Kentucky (68) by 17.2 at home. Kentucky has a 0.17 chance of beating South Carolina.

Arizona State (16) will beat Utah (46) by 6.2 on the road. Utah has a 0.36 chance of beating Arizona State.

Florida State (18) will beat Wake Forest (84) by 12.9 on the road. Wake Forest has a 0.23 chance of beating Florida State.

Georgia (19) will beat Tennessee (43) by 3.7 on the road. Tennessee has a 0.41 chance of beating Georgia.

Notre Dame (20) will beat Air Force (53) by 11.9 at home. Air Force has a 0.25 chance of beating Notre Dame.

Iowa (21) will beat Penn State (52) by 5.1 on the road. Penn State has a 0.38 chance of beating Iowa.

Virginia Tech (23) will beat Miami (FL) (41) by 8.1 at home. Miami (FL) has a 0.32 chance of beating Virginia Tech.

Pittsburgh (24) will beat Rutgers (75) by 8.3 on the road. Rutgers has a 0.32 chance of beating Pittsburgh.

Mississippi State (26) will beat UAB (103) by 16.4 on the road. UAB has a 0.18 chance of beating Mississippi State.

Illinois (27) will beat Indiana (100) by 15.5 on the road. Indiana has a 0.19 chance of beating Illinois.

West Virginia (29) will beat Connecticut (66) by 10.6 at home. Connecticut has a 0.27 chance of beating West Virginia.

Nevada (31) will beat UNLV (109) by 22.7 at home. UNLV has a 0.11 chance of beating Nevada.

Navy (32) will beat Southern Miss (64) by 9.7 at home. Southern Miss has a 0.29 chance of beating Navy.

Georgia Tech (33) will beat Maryland (60) by 8.5 at home. Maryland has a 0.31 chance of beating Georgia Tech.

Michigan (34) will beat Northwestern (70) by 4.7 on the road. Northwestern has a 0.39 chance of beating Michigan.

UCF (35) will beat Marshall (94) by 16.8 at home. Marshall has a 0.17 chance of beating UCF.

North Carolina (42) will beat Louisville (67) by 8.0 at home. Louisville has a 0.32 chance of beating North Carolina.

Baylor (47) will beat Iowa State (76) by 9.1 at home. Iowa State has a 0.30 chance of beating Baylor.

North Carolina State (48) will beat Central Michigan (96) by 16.6 at home. Central Michigan has a 0.17 chance of beating North Carolina State.

Western Michigan (55) will beat Bowling Green (101) by 15.3 at home. Bowling Green has a 0.19 chance of beating Western Michigan.

Toledo (57) will beat Eastern Michigan (117) by 25.4 at home. Eastern Michigan has a 0.08 chance of beating Toledo.

Northern Illinois (58) will beat Kent State (106) by 16.0 at home. Kent State has a 0.18 chance of beating Northern Illinois.

Oregon State (69) will beat Arizona (59) by 0.9 at home. Arizona has a 0.48 chance of beating Oregon State.

Brigham Young (61) will beat San Jose State (105) by 14.9 at home. San Jose State has a 0.20 chance of beating Brigham Young.

Florida International (62) will beat Akron (119) by 24.1 on the road. Akron has a 0.10 chance of beating Florida International.

Washington State (63) will beat UCLA (87) by 3.2 on the road. UCLA has a 0.43 chance of beating Washington State.

Utah State (65) will beat Wyoming (107) by 14.9 at home. Wyoming has a 0.20 chance of beating Utah State.

Houston (71) will beat East Carolina (88) by 7.3 at home. East Carolina has a 0.34 chance of beating Houston.

Syracuse (72) will beat Tulane (116) by 12.5 on the road. Tulane has a 0.24 chance of beating Syracuse.

Temple (74) will beat Ball State (110) by 8.4 on the road. Ball State has a 0.31 chance of beating Temple.

Troy (77) will beat Louisiana Lafayette (93) by 2.0 on the road. Louisiana Lafayette has a 0.45 chance of beating Troy.

Louisiana Tech (78) will beat Idaho (102) by 4.8 on the road. Idaho has a 0.39 chance of beating Louisiana Tech.

Ohio (79) will beat Buffalo (115) by 11.2 on the road. Buffalo has a 0.26 chance of beating Ohio.

Minnesota (82) will beat Purdue (92) by 0.5 on the road. Purdue has a 0.49 chance of beating Minnesota.

Arkansas State (86) will beat Louisiana Monroe (99) by 2.6 on the road. Louisiana Monroe has a 0.44 chance of beating Arkansas State.

Miami (OH) (89) will beat Army (91) by 3.1 at home. Army has a 0.43 chance of beating Miami (OH).

Florida Atlantic (97) will beat North Texas (112) by 1.2 on the road. North Texas has a 0.47 chance of beating Florida Atlantic.

Middle Tennessee State (108) will beat Western Kentucky (111) by 4.9 at home. Western Kentucky has a 0.39 chance of beating Middle Tennessee State.

Filed Under: Arkansas Razorbacks, Auburn Tigers, College Football, College Football 2011, College Football Analytics, Florida Gators, Football Analytics, LSU Tigers, Memphis Tigers, Nebraska Cornhuskers, Ohio State Buckeyes, Oklahoma Sooners, Rice Owls, Texas Longhorns

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