It's the offseason, and it's been a while since I've posted. Since there are no games to talk about, I thought I'd address an "advanced stats" issue that often comes up for debate - tempo free stats. Certainly my regular readers are more supportive of tempo free stats than most of the dinosaurs that call games on television or talk about them for major newspapers/magazines, but there's a myth that I wanted to explore about the relationship between efficiency and tempo.
Let's start with a couple of graphs that should make sense - offensive and defensive PPG vs raw tempo (possessions per game). The data below includes all 345 Division I teams from the 2011-12 season. I have thrown a best fit line on the data, with the equation in the bottom right hand corner. Don't worry about the y-intercept - what matters is the slope and the R-squared. If you forgot your high school statistics class, R-squared tells you how well the data fits the "best fit" line. So in this case, an R-squared of 1 would mean that all of the data fit perfectly on that line, and an R-squared of 0 would mean zero correlation (though for those of you that took some college stats, you'll know that for a finite-sized sample, even with no correlation you'd expect a tiny positive R-squared just from pure randomness). Anyway, check out the data below:
The first thing you see on those two plots is what you expect - the more possessions per game the more points per game a team scores and allows. In fact, the data says that for every extra possession per game, teams score 1.15 more points and allow 1.22 more points. And you can see that the fit, while obviously not perfect, is pretty good. Clearly, the faster you play the more points you score and the more you allow - I don't think this is disputed by anybody.
But what is disputed is whether tempo can affect efficiency. It's taken as objective truth by most basketball announcers and mainstream media analysts that it does. Teams that play slow can "grind" a game and "frustrate" an opposing offense, while teams that run can get more fast breaks and wear out opposing defenses. Well, is this true? Let's check out some data below:
In other words, the myth is wrong. Faster tempos do not make it easier to score, and slower tempos do not make it easier to defend. There are some very slow elite defenses (Wisconsin and Virginia being the most obvious examples from this past season) but there are also very quick elite defenses (North Carolina and Marquette come to mind from this past season). At the same time there were very quick elite offenses (Iona) and very slow elite offenses (Florida).
What's really fascinating to me is what I saw when I plotted Pomeroy efficiences vs point per game stats:
Naturally teams that are more efficient offensively score more points and teams that are more efficient defensive allow fewer points - that's pretty obvious. But compare the best fit lines to the two plots at the top of this post, which are PPG vs tempo. Scoring efficiency correlates with PPG a little bit better than tempo... but only a little bit. So if a team scores a ton of points per game, it tells you something about how good they are at scoring, but almost as much about how fast they play. Announcers during games routinely tell us that one of the teams we're watching is really good at scoring because they score a lot of points per game, or are really good at defense because they allow very few points per game, but it turns out this is only half the story. PPG tells us almost as much about tempo as it does about how good a team is on offense or defense.It's possible for an elite offense to score 65 ppg and for a poor offense to score 70 ppg - it happened this past season!
As an aside, staring at this data got me thinking about tempo vs team quality - do the best teams tend to run or tend to slow things down? Let's look at the data first:
Obviously some coaches have certain systems that they've honed over years, and these systems require fast or slow play. Force a Mike Anderson team to grind the ball and they won't play as well - same goes for asking a Mike Brey team to run. But for coaches that are more flexible in their system, or that are starting fresh, it might be worth considering a quicker or slower tempo depending on your team quality.
But if there's one takeaway from this post, hopefully it's that you get as irritated as I do when announcers tell us that PPG tell us how well a team plays offense or defense. If you're an analyst: ignore tempo and tempo-free stats at your own peril.