Conference efficiency margins and strength of schedule

A couple of my favorite basketball bloggers are big proponents of conference efficiency margin (what I normally call net efficiency).  Efficiency margin is simply the difference between points per possession scored and points per possession allowed.

Basketball Prospectus author John Gasaway, who may have pioneered this stat, offered a pithy explanation of it's utility last month:

Why track per-possession performance in league play?

Over the next eight to nine weeks these 126 teams will play over a thousand possessions each. Half of those possessions will take place at home, and half of them will occur on the road. All of that basketball will be played against opponents that by conference affiliation have been designated as nominal equals in terms of programmatic resources. (Though, granted, a league like the A-10 certainly exhibits some notable diversity in terms of member heft.) And, not least, all of that basketball will take place in increasingly close temporal proximity to the NCAA tournament.

And greyCat over at Villanova by the Numbers has been tracking these stats for the Big East biweekly, and in great detail.  Mr. Cat (I actually do know his name, but I'm not telling) also provided an important caveat before jumping into the numbers with his latest posting

I understand the argument against looking only at (for example) conference games -- the sample is too small, the schedule is unbalanced, the time-frame is too restricted, etc. etc. etc. -- all of which are valid points.

I actually took a look at this very point last season around this time, and it turned out to be more more informative than I realized at the time.  I'll come back to why that is at the end, but first I thought I'd re-run that analysis tonight.

I've compiled the strength of schedule for all Big East teams for conference games played so far (through Monday, Feb 1st), and plotted eff. margin against strength of schedule. Here, I'm using KenPom's Pythagorean rating (0-1), rather than his ranking (1 to 347) for the strength of schedule calculation.  The strength of schedule is weighted for home vs. road games.  The efficiency margin stats come from StatSheet.com.

Here we go (click to enlarge):

Just as we saw last year, there is a strong correlation between conference strength-of-schedule played to date and the efficiency margin posted.  So teams such as West Virginia and Villanova, which currently lead the league in efficiency margin are definitely getting some help from a soft early-season schedule, while Seton Hall is a bit below water thanks in no-small-part to a brutal start from the schedule-makers.

Now a bit of that effect is circular, in the sense that good teams don't have to play themselves, and therefore their schedules are slightly easier on average, while bad teams schedules are harder because they're missing an easy opponent (themselves).

However, in any league with an unbalanced schedule like the Big East, these effects are only one part of the overall scheme that won't entirely even out at the end.  For example, our own Georgetown Hoyas have been rewarded this year with home-and-away series with the current AP-ranked #2 and #3 teams.

Here's a table summarizing the conference season so far, and what's left for each team (rankings are from hardest to easiest):

.                      Current           Remaining          Exp. Final
Team                  SOS    Rank        SOS    Rank        SOS    Rank
Cincinnati           0.825    15        0.902    3         0.868    14
Connecticut          0.878    6         0.862    11        0.870    11
DePaul               0.913    2         0.823    14        0.875    6
Georgetown           0.867    10        0.876    8         0.872    10
Louisville           0.882    5         0.872    9         0.877    4
Marquette            0.890    4         0.819    16        0.858    16
Notre Dame           0.856    11        0.892    5         0.875    7
Pittsburgh           0.873    9         0.878    7         0.876    5 
Providence           0.812    16        0.936    1         0.888    1
Rutgers              0.910    3         0.838    13        0.879    3 
Seton Hall           0.919    1         0.819    15        0.872    9
South Florida        0.873    8         0.860    12        0.867    15
St. John's           0.877    7         0.864    10        0.870    12
Syracuse             0.851    12        0.885    6         0.869    13
Villanova            0.845    13        0.911    2         0.886    2
West Virginia        0.839    14        0.897    4         0.874    8 

Seton Hall has had the pleasure of playing the toughest Big East schedule so far, and are showing the effects with a 3-5 record.  They're path will get much easier, so expect them to make a push towards legitimacy.  DePaul and Rutgers have also had tough early-season slates, but I'd think the best they can hope for is just a step up from the absolute dregs of conference efficiency margin (anything worse than -20 is really bad).

Providence has a brutal second-half schedule, harder than what any team has played so far.  Many had pegged the Friars to be one of the worst teams in the league this year due to the loss of so many players, and that result may still be coming.  Meanwhile the Big East's Big Three (Villanova, Syracuse and West Virginia) have all benefited from relatively easy first-halves and should all see things get a bit tougher the rest of the way.  In fact, Syracuse may be in the best position of the three to win the regular-season conference title because of this.

It's also worth noting that the spread between easiest expected final schedule (Marquette) and hardest (Providence) is about the equivalent of the difference between playing U of Miami or UConn on a neutral floor, respectively (i.e. not really that much).


Finally, returning to that bit about what was so informative about last year's plot (reproduced below).  It turns out that teams that met two conditions went on to the NCAA tournament:

1. They sat above the fitted line, i.e. were better than average, adjusted by schedule strength.
2. They already had positive efficiency margins midway through the season.

So, right now, it looks like there are seven teams in good position for March (Villanova, West Virginia, Syracuse, Georgetown, Louisville, Marquette (!), and Pitt).  There are three other teams that meet only one of those criteria: Cinci, UConn and Seton Hall.

Here's last year's plot (from 24-Jan-09):