John David Mercer-USA TODAY Sports
A statistical comparison between Nebraska's dynasty from 1993-1997 and Alabama's current run from 2008-2012. The comparison is done to answer which team had a better run.
The first part of this analysis was published in January. The second and third parts, however, had not been published yet, and as we had done a re-work of the graphics, we felt it best that we publish the article in full.
There are myriad ways to compare the five-year dynasties that Nebraska and Alabama have put together. Some indicate Nebraska's was more impressive, while others tend to favor Alabama. This is my attempt to compare the two using defensible statistical analysis. It is not the final word on this issue; I'm doing it simply to attempt to get at the question of who accomplished more during their five-year run.
I organized the analysis along offense, defense, margin of victory, win/ loss record, and strength of schedule.
Where I state that there is sufficient evidence to conclude ' X', the statement is based on standard hypothesis testing (t-tests) and evaluated at the alpha =.10 level of significance. The conclusions I draw regarding win/loss records and the overall conclusions are subjective and not based on hypothesis testing.
This first chart illustrates the average points that Nebraska/Alabama scored when you categorize opponents by end of season ranking. For simplicity sake, I used the end of season Congrove Composite Index. Using the end of season ranking is better because it is available and goes a long way towards to identifying teams that were ranked at one point in the season but should not have been or who were unranked or lower ranked but proved to be better that season.
The number next to each point on the graph is the number of games Nebraska/Alabama played against teams of that rank.
As you would expect, as the opponentsí rank goes down, the average score that the two teams scored climbs. For opponents of all ranks, Nebraska's average points scored is markedly higher. For all ranks, the average Nebraska score is 42.82 and the average Alabama score is 33.84. There is sufficient evidence to conclude that Nebraska's offense was superior to Alabama's.
This next chart compares the two teams' scoring as a percentage of the average scoring allowed by their opponents. While this is much the same as the chart above, it factors in the additional information of their opponent's defenses. Obviously, if Nebraska's average scoring difference came because it played a five-year slate of defensive duds then the argument that Nebraska scores more points is suspect.
Considering Nebraska and Alabama's scoring as a percentage of their opponentsí scoring defense, one would expect that the percentage would remain basically steady, or show a slight increase as the rank of an opponent decreases. This, however, does not seem to be the case. If anything, there is a slight negative correlation between percentage scored and opponent rank.
It's difficult to say why this is the case, but I would speculate that it's because 150% of an opponent ranked 1-10 is, in real points, much less than 150% of an opponent ranked 100-110. These games would be the times that 3rd and 4th string is played, which sometimes leads to offensive mistakes and garbage time points for the opponent.
The flatter trend of the Alabama line may indicate that the Crimson Tide was more consistent on offense than the Huskers over the five years. While the Crimson Tide did not put up the sheer number points that the Huskers did, their offensive production was remarkably steady. Nebraska, on the other, was less consistent, and their performance against teams ranked 101-110 actually underperformed Alabama's comparably ranked opponents. This not withstanding, there is sufficient evidence to conclude that Nebraska's offense was superior to Alabama's.
Margin of Victory
As one would expect, the average margin of victory by both teams increases as their opponents' rank decreases. Both show a steady and reasonably linear relationship between average MOV and opponent rank. The exception is Nebraska's average MOV against opponentís ranked 21-30. This is because there are only two games here, and Nebraska lost one of them, leading to a much smaller average.
Generally, we can state that both teams did what great teams as supposed to do they consistently beat other teams up. As their opponentsí rank decreases, those beatings are more severe. It's worth noting that Nebraska's average margin of victory against teams ranked 1-10 was 2.5 times that of Alabama's (17.5 vs 6.3). Against teams ranked 11-20, Nebraska's average MOV was almost three times that of Alabama, (20.0 vs 7.3). For opponents of all ranks, Nebraska's average MOV was
18.87 28.2 points and Alabama's average MOV was 16.40 22.0 points. Nebraska's superiority in offense and the insignificant difference in offense results in an average MOV that favors the Huskers.
Th is next chart illustrates a very similar comparison to Offense 1, but it compares the defenses that both teams put on the field by measuring the average opponent score, again broken down by end of season rank. As above, the numbers on the chart indicate the number of teams Nebraska and Alabama played in that rank group.
For teams ranked in the top-10, the difference in scoring defense is small. For Nebraska, it is 18.2, for Alabama, 20.2. For most other opponent rank categories Alabama has a slight performance advantage, ranging from about 3-7 points. For opponents of all ranks, Nebraska's opponents averaged 14.41 points and Alabama's opponents averaged 11.82 points. There is insufficient evidence to to identify defense as better than the other over the entire five years.
The data points illustrated in the next chart are the average opponents' score as a % of the teams' season scoring defense. A lower percentage indicates a better performance.
At first blush, I would have expected there to be a negative correlation between the average percentage score by an opponent and the opponent's rank... better opponents should do better offensively against either team than crummy opponents would. Both teams' opponent scoring shows this general trend, with a decreasing effect as the quality of opponent decreases. This might be explained by the fact that games against far inferior opponents present opportunities to play the third and fourth string, often meaning the opponent has opportunities to score that would not have otherwise been presented had the starters remained in the game.
Nebraska's defensive performance shows no obvious correlation between rank and opponent points. Alabama, shows a strong negative correlation between Opponent rank and the percent of scoring they allowed their opponents. In other words, Alabama held inferior opponents to well under their season scoring offense average but gave up points to highly ranked teams.
For opponents of all ranks, Nebraska opponents' average score as a % of scoring defense was 102%. Alabama opponents' average score as a % of scoring defense was 101%. As with Defense 1, there is insufficient evidence to conclude that one defense is better than the other.
Wins and Losses
This one is simple: Nebraska had a better overall W/L% (95.2% vs 89.6%) and a much better win percentage versus top-20 teams (95% vs 83%). Nebraska also had three undefeated seasons, Alabama had one defeated season. Twice Nebraska's win % dipped to 92% for the season (93 and 96). Alabama had four seasons at or below 92% (08-86%, 10-75%, and 11-92%).
For Alabama, six of their seven losses (86%) were to teams ranked 1-20 (UF-2008-#1, Utah-2008-#4, Auburn-2010-#2, LSU-2011-#2, LSU-2010-#11, and A&M-2012-#5) while two of Nebraska's three losses (67%) were in the top 20 (FSU-1993-#1, ASU-1996-#4).
Alabama and Nebraska both lost to one team ranked 21-30 (South Carolina-2010-#27 and Texas-2006-#25)
Looking at where losses occurred, Alabama lost three at home, two in Bowl/CCG's, and two away. Nebraska lost zero at home, one away, and two in Bowl/CCGs.).
Though it is a subjective assessment, Nebraska's three und efeated seasons, zero home losses, and the same number of bowl and conference championship game losses is sufficient to conclude that Nebraska's Win/Loss record is better than Alabama's.
Strength of Schedule
Considering the season average rank of opponents, Nebraska's five year season average opponent average is 48.29 while Alabama's is 53.82. There is sufficient evidence to conclude that Nebraska's average season opponent ranking was more difficult than Alabama's. I t follows, therefore, that Nebraska's dynasty was established during seasons of greater difficult than Alabama's.
Combined with Nebraska's advantage in W/L record, this may present the strongest evidence that Nebraska's dynasty was more impressive than Alabama's. It is hard to ignore that Nebraska's three undefeated seasons were all more difficult than the average of the 10 seasons considered, while Alabama's were less difficult than the average of the 10 seasons considered. Bama's one season more difficult than average was 2010, the season in which Bama lost three games and finished with a .75 W/L record. Finally, the most recent two seasons, in which the Crimson Tide claimed its back to National Championships, were the two least difficult seasons considered in this analysis.
Nebraska was better on offense; neither team demonstrated a clear superiority in defense; and Nebraska had a better W/L record and a stronger average strength of schedule.
I'll allow my readers to make the final conclusions. Who has the best five-year dynasty?