The Influence of the AP Preseason College Football Poll
A few weeks ago I looked at how the preseason college football poll influences the rankings at the end of the year. I found that for the most part, the teams that ranked higher in the preseason tend to be ranked higher going into the postseason. So if Team A and Team B both finish the regular season undefeated, the team that was ranked higher in the preseason tends to be the one ranked higher going into the postseason.
The biggest exception was, and I hope you’re sitting down for this, SEC teams. SEC teams that finished the regular season with 0 or 1 loss tended to be ranked higher than non-SEC teams with the same amount of losses, regardless of the preseason poll. On the other side, Boise State (a team from a smaller conference) tended to get jumped by teams with the same number of losses that were ranked lower than them in the preseason poll. And the oddball was USC, who in both 2007 and 2008 was jumped by 4 different teams despite starting the season ranked lower than the Trojans and finishing the regular season with the same number of losses.
Looking at 2014
Now let’s turn our attention to this season. Are the same trends happening? There are currently 10 undefeated teams. I looked at the order those 10 teams were ranked in the preseason AP Poll and the order they are currently ranked in the AP Poll. Below is an individual value plot of the data that shows each team's preseason rank versus their current rank.
Teams on the diagonal line haven’t moved up or down since the preseason. So of the 10 undefeated teams, Florida St and Auburn were ranked #1 and #2 respectively in the preseason. And they remain that way currently.
Teams above the line have jumped teams that were ranked ahead of them in the preseason. Just as we saw before, it’s the SEC teams that rise to the top regardless of where they were ranked in the preseason. Mississippi State had 22 points in the AP preseason poll, which is actually one less than TCU received, and weren’t even close to being in the top 25. But now? They have 1,320 points, are ranked 3rd, and jumped 5 other undefeated teams that were ranked higher than them in the preseason. It’s good to win games in the SEC.
Teams below the line have been jumped by teams ranked lower than them in the preseason. Baylor and Notre Dame are simply casualties of the Mississippi teams. If somebody moves up, somebody else has to move down. But Marshall appears to fit our “Boise State” profile, as they are a team from a small conference. They received 41 points in the preseason AP Poll, putting them just outside the top 25. And now, despite being 5-0, they have only 78 points and are the only undefeated team still outside the top 25.
Measuring Correlation and Concordance
It appears that the preseason poll is influencing the current rankings, but we can get some statistics to confirm our hunches. The first is a correlation coefficient. The correlation coefficient can range in value from -1 to +1. The larger the absolute value of the coefficient, the stronger the relationship between the variables. An absolute value of 1 indicates a perfect relationship, and a value of zero indicates the absence of relationship.
For these data, both values equal about 0.685, indicating a positive association between preseason rankings and the current rankings. Teams ranked higher in the preseason are also currently ranked higher.
We can also look at the concordant and discordant pairs. A pair is concordant if the observations are in the same direction. A pair is discordant if the observations are in opposite directions. More concordant pairs means voters are keeping the same order as the preseason, while more discordant pairs means they’re switching teams.
Of the 45 pairs of teams, 35 of them are concordant, meaning most of the time voters are keeping teams in the same order as the preseason. The 10 discordant pairs all involve either Mississippi, Mississippi State, or Marshall. So it’s pretty clear when voters are switching teams from the preseason.
Implications for the College Football Playoff
So far we’ve shown that voters in the AP Poll prefer to keep the same order teams are ranked in the preseason, minus SEC teams and teams from smaller conferences. But the voters of the AP Poll won’t decide the teams in the college football playoff, a separate college football playoff committee will. Luckily for us, that committee will start releasing their own set of rankings on October 28. So we’ll come back then and see if the committee is also influenced by preseason rankings the same way the AP voters are.