Measuring Vertical Impact
by Ken Pomeroy
AuthorThere are several physical traits valued in basketball, but none is more unique to the sport than height. You can t get through a televised game these days without hearing how long a particular player is. Indeed, a basketball floor containing 10 Division I players is quite unlike the general population. According to the National Center for Health Statistics, the average height of an adult male in America is 5 9 . Only two percent of college basketball players seeing minutes this season are 5 9 or less. Clearly height is a valuable trait in this game, and it s valued highly by college coaches. There s plenty of evidence for that, and none better than the fact that coaches will take a chance on a seven-footer with limited skills while never doing the same for a six-footer.
So in an effort to examine what a few extra inches mean, I ll be tracking the average height of each D-I team for the rest of the season. I m computing a minutes-weighted average height using every player that plays at least 10 percent of his team s minutes. Because of injuries, suspension and other eligibility issues, these numbers will fluctuate slightly as the season progresses. For instance, Stanford and Louisville will appear to get taller as Brook Lopez and David Padgett, respectively, continue to get minutes after missing a large chunk of time early in the season. There are a few limitations–in a perfect world, it would be nice to use wingspan instead of height–but this at least gives us a crude estimate to rank teams by their vertical dimension. So what does height really mean?
It should be no surprise that a team s average height does correlate to its offensive and defensive prowess. On the offensive side, average height has a correlation coefficient of .27 to adjusted efficiency, and on the defensive side it s .38. For those new to correlation, a value of 1 would mean that variation in height would explain all the variation in efficiency. A correlation coefficient of zero means that the two values are entirely unrelated. So in layman s terms, there s a relationship between height and efficiency on both ends of the floor, but it s not very strong. In addition, the relationship between height and efficiency is stronger on the defensive end.
This analysis gets a little more sophisticated if we break down height by position. For the purposes of quickly analyzing 341 teams, I m deriving average height by position by assuming that the tallest 20 percent of player-minutes are being used at center, the next tallest 20 percent of minutes at power forward, etc. Obviously this does not always match reality, but in order to process this much data, it s not feasible for me to sort out all of the Pat Calatheses of the nation and put them in their proper position.
It turns out this endeavor is worthy of the effort, because there is a much better relationship between most tempo-free team stats and height if we ignore the shortest 60 percent of player-minutes. Here are the categories that have the strongest relationship to effective height:
1. Block Pct. .486
2. 2-pt% defense .478
3. eFG% defense .451
4. adjusted defensive efficiency .420
There are a couple points worth making here. First, defensive stats have a much better correlation with height than their offensive counterparts. Second, the only stat I adjust for competition right now is efficiency. Presumably, we could squeeze out a slightly better relationship to height by adjusting the top three metrics for the quality of the opponent.The deeper message here is that all those coaches lusting after seven-footers with hands of stone and happy feet don t have the wrong idea. They may end up getting a defensive presence that the vertically challenged can t provide. Conversely, coaches shouldn t be so quick to pass on a short kid simply because of his height, especially if his team already has some size up front. So Oregon coach Ernie Kent had the right idea by pursuing 5 6 Tajuan Porter to fill the shooting guard position for four seasons. (Another advantage of recruiting the undersized–if they turn out to be stars, they ll be around for four years. The NBA hates a lack of size.) Coaches obsessing about size in their backcourt probably should back off. It depends on the system being run, of course, but small guards do not have to translate into a weak defense.
Second-year Nebraska coach Doc Sadler deserves to be recognized for trying to prove this principle, even if he may not be aware of it. The two Cornhuskers guards that have received the most minutes to date are 5 7 freshman Cookie Miller and 5 11 sophomore Jay-R Strowbridge. In terms of average height, Nebraska currently ranks 317th in the country, the shortest power conference team in the land. However, in effective height–averaging the minutes at the center and power forward position–they are a respectable 113th, and their adjusted defensive efficiency ranks 11th. This is a ranking that will probably drop in conference play, as the Huskers and 6 11 center Aleks Maric have piled up gaudy numbers against the dregs of Division I. But based on performances against Oregon, Creighton and Arizona State, Nebraska will make offenses struggle in Big 12 play.
Sadler s team shows that there is room for short people in this game, but let s not get carried away. It really pays to have size up front. Of the teams that entered Wednesday s play in the top 20 in adjusted defensive efficiency, only one had an effective height below the national average–and barely so, by two-tenths of an inch.
That team is Duke, which has gone short and up-tempo this season. It s an approach that has resulted in a noticeable improvement offensively without sacrificing defense, at least so far. However, for most teams a great defense requires size at the four and the five. At least on the defensive end, basketball really is a big man s game.
Ken Pomeroy is an author of Basketball Prospectus. You can contact Ken by clicking here or click here to see Ken’s other articles.