Tuesday, February 15, 2011

Why Princeton's Adjusted Efficiency Margin Might Be Deceiving

The best team in the Ivy League at the 14-Game Tournament halfway pole?

Both the simple metrics (standings) and more complex statistics (adjusted efficiency margin) agree: It's Princeton.

The only place they differ is by how much. The Tigers hold a slight half-game lead (one game in the loss column) over Harvard in the league standings, but Princeton's +11.1 adjusted efficiency margin is double the Crimson's +5.5.

In this case, however, the win-loss stat may be closer to the real story than the efficiency one, due to a wildly divergent, yet uncontrollable underlying factor.

A dominant big man can absolutely change a game. His mere presence in the paint can make diminutive guards think twice about driving the lane and any one that dares attempt such a bold maneuver will often have his shot altered or rejected altogether.

A lanky, quick perimeter player can also change a game. With a long wingspan, the guard can frustrate opponents by getting his hands in the face of shooters or even getting a touch to the ball as they attempt to fire jumpers.

In this way, a team is directly responsible for its two-point and three-point shooting defense. If it frustrates opposing offenses, it can drive those numbers down. If it yields open shots, it can expect those numbers to balloon.

But there's one place on the floor you can't guard, and it is of vital importance to the outcome of games.


In conference play, Ivy teams are making 71.8 percent of their free throws (a full three percentage points above the national average). Assuming that teams can't do anything to "defend" the line, given that all of the teams have basically played the same set of opponents, each team's free throw percentage allowed should hover around that average mark.

Four Ivy teams have yielded opposing free throw shooting percentages between 70.2 and 73.3 percent - Brown, Cornell, Penn and Yale. The other four teams are all over the place. Columbia and Princeton have been relatively lucky (opponents are hitting at 65.5 percent and 63.2 percent, respectively) while Dartmouth and Harvard have been terribly unlucky (opponents are converting at 77.1 percent and 81.4 percent, respectively).

While that's an interesting stat, what we really want to know is the impact in terms of pure points per game and, more importantly, the impact that the free throw percentage against disparity is having on those league adjusted efficiency margins.


Here are the current adjusted efficiency margins by team during Ivy play:

AdjORat AdjDRat AdjEffMar
Brown 98.0 104.9 -7.0
Columbia 99.9 103.3 -3.4
Cornell 99.4 104.7 -5.2
Dartmouth 82.7 102.5 -19.8
Harvard 107.1 101.6 5.5
Penn 98.8 98.2 0.6
Princeton 102.8 91.7 11.1
Yale 97.4 97.0 0.5

As mentioned above, Princeton has a huge lead on the rest of the field, including second place Harvard. Penn and Yale are tied for third, while Cornell has closed the gap on Columbia for fifth.

If we adjust the defensive efficiency to bring every team's free throw percentage against to the league average of 71.8 percent, things change quite a bit for those squads whose figures deviated sharply from that mean.

AdjORat AdjDRat AdjEffMar
Brown 98.0 105.4 -7.4
Columbia 99.9 105.3 -5.3
Cornell 99.4 104.2 -4.7
Dartmouth 82.7 100.9 -18.2
Harvard 107.1 99.8 7.3
Penn 98.8 97.8 1.0
Princeton 102.8 94.2 8.7
Yale 97.4 96.6 0.8

Princeton's +11.1 margin shrinks to +8.7 and Harvard's rises from +5.5 to +7.3, narrowing the gap between the two from 5.6 points per 100 possessions to just 1.6. The reason why the Crimson's outrageously poor free throw "defense" doesn't hurt it more stems from the fact that Harvard is the sixth stingiest team in the nation in terms of doling out trips to the line and by far the best in the conference at keeping opponents from the stripe. Fewer opposing attempts means fewer points, even if the opponents connect at a high percentage.

The other notable change is that upon adjusting Columbia's free throw percentage against to the mean, the Lions' efficiency margin falls below that of Cornell.


Every Ivy League race comes with its own story, and thus far, the narrative has depicted a consistently dominating Princeton defense edging out a Harvard unit that can't stop teams from lighting it up from three. Thus, we see the difference between the Crimson's 101.6 adjusted defensive rating and the Tigers' 91.7.

The reality isn't quite that stark. Harvard's three-point shooting defense has gotten worse in Ivy play, because Ivy teams shoot relatively better from behind the arc than they do from inside it (thus why the Crimson's two-point defense has correspondingly strengthened in league play). The entirety of the difference between Harvard's non-conference and conference defensive ratings can be accounted for in the free throw percentage against differential.

Princeton will continue to be the better defensive team, and the Tigers have indeed stiffened in league play even after adjusting for the free throw luck. But once we take into consideration that free throw differential, it's clear that the Tigers' defensive advantage is only slightly greater than the Crimson's offensive advantage, meaning that the league race might not be as one-sided as the initial adjusted efficiency numbers would lead one to believe.

No comments:

Post a Comment