Steve Ertel

Precision on the court. Curiosity in the classroom. That’s the AND in Vanderbilt University. 🏀⚓️⬇️

My second favorite college football team, Vanderbilt, may be getting a raw deal from the CFP committee—like, maybe it should be ranked as high as 6th, rather than 14th. Below is my “Common Opponent” analysis. Common Opponent Analysis: Why the CFP may be Severely Underrating Vanderbilt Tim Groseclose Dec. 6, 2025 In this document I use what I call Common Opponent Analysis to compare Vanderbilt with other teams that are ranked among the top 25 in the College Football Playoff ranking. As the analysis shows, the current CFP ranking seems to place Vanderbilt significantly worse than the rank it may deserve. Defining the Method, an Example To illustrate the method, let us first consider one team, Oklahoma, as an example. Oklahoma and Vanderbilt had seven common opponents: Texas, Auburn, South Carolina, Tennessee, Alabama, Missouri, and LSU. Vanderbilt lost to Texas by 3 points. Importantly, however, Texas was the home team in the game. Various analyses have estimated the home-field advantage to be approximately 3 points. Thus, if we discount home-field advantage, the game suggests that—on a neutral field—Vanderbilt and Texas would be evenly matched. That is, Texas is 0 points better than Vanderbilt. Meanwhile, Oklahoma lost to Texas 23-6. The game was played on a neutral field. Thus, the game suggests that Texas is 17 points better than Oklahoma. If we combine the two games---Oklahoma v. Texas and Vanderbilt v. Texas---they suggest that Vanderbilt is 17 points better than Oklahoma. If we consider the other six common opponents, the games imply other amounts by which Vanderbilt is better or worse than Oklahoma. Indeed, some of the games suggest that Vanderbilt is worse than Oklahoma. Using the above method on the other six opponents respectively gives the following amounts by which Vanderbilt is better than Oklahoma. (A negative number indicates that---using the two games of the particular common opponent---Oklahoma is better than Vanderbilt.). Auburn, 0; South Carolina, 5; Tennessee, 15; Alabama -18; Missouri, -2; LSU 3. Finally, I compute the average of the above seven numbers. It equals 2.86. (Specifically [17+0+5+15-18-2+3]/7 = 20/7.). Thus, the Common Opponent Method implies that Vanderbilt is 2.86 points better than Oklahoma. Results: How the Common Opponent Method Rates Vanderbilt Against Other Teams in the CFP Top 25 Not counting Vanderbilt, there are 24 teams in the CFP top 25. Of these 24 teams, ten had at least one common opponent with Vanderbilt. I list these teams, their current ranking in the CFP, the common opponents that the team shared with Vanderbilt, and how the Common Opponent Method Rates the team against Vanderbilt. 1. Ohio State. Vanderbilt and Ohio State had one common opponent, Texas. The Common Opponent Method rates Ohio State as 4 points better than Vanderbilt. 3. Georgia. Vanderbilt and Georgia had five common opponents: Tennessee, Alabama, Kentucky, Auburn, and Texas. The Common Opponent Method rates Georgia as 3.8 points better than Vanderbilt. 6. Ole Miss. Vanderbilt and Ole Miss had three common opponents: Kentucky, LSU, and South Carolina. The Common Opponent Method rates Vanderbilt as 10.33 points better than Ole Miss. 7. Texas A&M. Vanderbilt and Texas A&M had six common opponents: Utah State, Auburn, LSU, Missouri, South Carolina, and Texas. The Common Opponent Method rates Texas A&M as 1.33 points better than Vanderbilt. 8. Oklahoma. Vanderbilt and Oklahoma had seven common opponents: Texas, Auburn, South Carolina, Tennessee, Alabama, Missouri, and LSU. The Common Opponent Method rates Vanderbilt as 2.86 points better than Oklahoma. 9. Alabama. Vanderbilt and Alabama had five common opponents: Missouri, Tennessee, South Carolina, LSU, and Auburn. The Common Opponent Method rates Vanderbilt as 3 points better than Alabama. (It should be noted that Vanderbilt and Alabama actually played each other. In that game Alabama won by 16 points. Alabama, however, was the home team. Thus, if we discount the home-field advantage, the score suggests that Alabama is 13 points better than Vanderbilt. It should also be noted that Alabama scored a “junk” touchdown at the end of the game. That is, Alabama, trying to run out the clock, did a run play near the end of the game. Vanderbilt, possibly trying to strip the ball from the runner rather than making a safe tackle, allowed the runner to score a lucky touchdown. The play illustrates (i) that Alabama more accurately is only about 6 points better than Vanderbilt and (ii) in any game there are many random incidents that can cause the score to misrepresent the true degree by which one team is better than the other. For this reason---and because the Common Opponent Method often involves a larger sample of games---the Common Opponent method might actually be a better method than using a head-to-head matchup of the two teams.) 12. Miami. Vanderbilt and Miami had one common opponent, Virginia Tech. The Common Opponent Method rates Vanderbilt as 7 points better than Miami. 13. Texas. Vanderbilt and Texas had one common opponent, Kentucky. The Common Opponent Method rates Vanderbilt as 19 points better than Texas. (It should be noted that Vanderbilt and Texas actually played each other. In that game Texas won by 3 points. Texas, however, was the home team. If we discount the home-field advantage, the game suggests that Texas and Vanderbilt are equally matched. It should also be noted that at the end of the game Vanderbilt recovered an onside kick, however did so just barely out of bounds, which gave the ball to Texas. Importantly, if the ball had bounced a few millimeters differently, then Vanderbilt would have recovered the ball in bounds and would have had another chance to score. The incident is another example of the random factors in a football game, thus suggesting the importance of a larger sample size, as the Common Opponent Method uses, rather than a sample of one, as a head-to-head matchup uses.) 17. Virginia. Vanderbilt and Virginia had one common opponent, Virginia Tech. The Common Opponent Method rates Vanderbilt as 10 points better than Virginia. 22. Georgia Tech. Vanderbilt and Georgia Tech had one common opponent, Virginia Tech. The Common Opponent Method rates Vanderbilt as 15 points better than Georgia Tech. Additional Notes Notre Dame is number 10 in the CFP rankings. Although Notre Dame and Vanderbilt had no common opponents, Notre Dame played Texas A&M and Miami. After discounting home-field advantage, the games suggest that Notre Dame is even with Miami, while Texas A&M is 2 points better than Notre Dame. As I note above, the Common Opponent Method rates Vanderbilt as 7 points better than Miami. If Notre Dame is even with Miami, this suggests that Vanderbilt is 7 points better than Notre Dame. As I note above, the Common Opponent Method rates Texas A&M as 1.33 points better than Vanderbilt. If Texas A&M is 2 points better than Notre Dame, this suggests that Vanderbilt is .67 points better than Notre Dame. The average of the above two numbers is 3.84 ( = [7+.67]/2), thus suggesting that Vanderbilt is 3.84 points better than Notre Dame. Michigan is number 19 in the CFP rankings. Although Michigan and Vanderbilt had no common opponents, Michigan played Oklahoma and Ohio State. After discounting home-field advantage, the games suggest that Oklahoma is 8 points better than Michigan, and Ohio State is 21 points better than Michigan. As I note above, the Common Opponent Method rates Vanderbilt as 2.86 points better than Oklahoma. If Oklahoma is 8 points better than Michigan, this suggests that Vanderbilt is 10.86 (=8+2.86) points better than Michigan. As I note above, the Common Opponent Method rates Ohio State as 4 points better than Vanderbilt. If Ohio State is 21 points better than Michigan, this suggests that Vanderbilt is 17 points better than Michigan. The average of the above two numbers is 13.93 ( = [10.86+17]/2), thus suggesting that Vanderbilt is about 14 points better than Michigan. Tulane is number 20 in the CFP rankings. Although Tulane and Vanderbilt had no common opponents, Tulane played Ole Miss. After discounting home-field advantage, the game suggests that Ole Miss is 32 points better than Tulane. As I note above, the Common Opponent Method rates Vanderbilt as 10.33 points better than Ole Miss. If Ole Miss is 32 points better than Tulane, this suggests that Vanderbilt is 42.33 (=32+10.33) points better than Tulane. Georgia Tech is number 22 in the CFP rankings. Although Georgia Tech and Vanderbilt had no common opponents, Georgia Tech played Georgia. After discounting home-field advantage, the game suggests that Georgia is 7 points better than Georgia Tech. As I note above, the Common Opponent Method rates Georgia as 3.8 points better than Vanderbilt. The difference in the two numbers suggests that Vanderbilt is 3.2 points better than Georgia Tech.