Because xHPI takes into account both margin of victory and quality of opponent in creating a score for each team in each game, a team’s rating will change at least slightly every time one of its opponents plays a game. In fact, since that opponent’s quality rating is based on its schedule, each team’s rating changes every time its opponents’ opponents play a game.
Most of the time those changes are very small, and the multiple changes that multiple opponents (and their opponents, in turn) bring into a team’s ranking tend to roughly cancel one another out. This is particularly true in conference play, when generally half of a team’s conference opponents win in any given week, and half of them lose. However, at times, these opponents’ outcomes can all largely align in one direction to produce relatively large swings in a team’s score relative to other teams. Such an occurrence often happens in bowl season, when a conference has a particularly strong (or weak) performance in bowl games.
And, of course, the point spreads that xHPI projects are based on the relative scores of the two teams. So when I calculated the point spread for the National Championship game, I decided to take a look at how the spread evolved over the bowl season. The results are presented in the chart below.
At the end of the regular season, Alabama and Clemson were ranked #1 and #2, respectively. xHPI projected a margin of victory of 3.8 points for the Crimson Tide. The early bowl games featured more success for the SEC (3-1) than the ACC (3-3); consequently, the point spread grew to 4.95 points. The spread grew to 5.2 points after New Year’s Eve’s first game, the Peach Bowl, in which Florida State lost to Houston.
While both Alabama’s and Clemson’s ratings increased after their victories in the semifinal games, Alabama saw the bigger jump after its more impressive victory, and, as a result, the point spread jumped by more than a point, to 6.44.
New Year’s Day brought two SEC victories and one SEC defeat, plus one quasi-ACC (Notre Dame) defeat. The point spread increased another third of a point, to 6.8. Georgia and Arkansas victories on January 2 resulted in a final jump of .18 points, raising the final point spread to 6.98 points. All-in-all, Alabama’s projected margin of victory increased by 3.18 points. Of that increase, only 1.24 points, or less than 40% of the change, was due to the semifinal games.