## Statistics of the week: Euroleague Simple Rating System

It is quite a wide-spread theory among stat geeks that when doing a club ranking for the major Northamerican professional leagues, it is favourable to go by point differential, not wins or losses. This makes perfect sense if you consider basketball, a game that consists of almost 200 team possessions per contest in the NBA and a little over 140 in the Euroleague, a continuous display of quality (or lack thereof) on both ends of the floor, instead of bringing it down to two options (win or loss) after 40 minutes of play versus a particular opponent.

However, there are things to consider. Pure point differential sounds perfect for just about any European domestic regular season, where every team has exactly two games versus the league’s other teams. Everyone has the same opponents. However, with regional divisions like in the NBA, the pure point differential (as is the win/loss-column) is noisy due to the fact that you are having more games against teams from your division and your conference, than against those from another conference. It is even more extreme in the Euroleague, where success might be enabled or made difficult simply by the quality of the opponents (or lack thereof) the draw assigns to you. A ranking that considers opponent quality would be far more meaningful.

This is where “simple rating system”, developed by and comprehensively explained over at pro-football-reference, comes into play. Quoting the explanation:

The idea is to define a system of 32 equations in 32 unknowns. The solution to that system will be collection of 32 numbers and those numbers will serve as the ratings of the 32 NFL teams. Define R_ind as Indianapolis’ rating, R_pit as Pittsburgh’s rankings, and so on. Those are the unknowns. The equations are:

R_ind = 12.0 + (1/16) * (R_bal + R_jax + R_cle + . . . . + R_ari)

R_pit = 8.2 + (1/16) * (R_ten + R_hou + R_nwe + . . . . + R_det)

…

One equation for each team. The number just after the equal sign is that team’s average point margin. […]

So every team’s rating is their average point margin, adjusted up or down depending on the strength of their opponents. Thus an average team would have a rating of zero. Suppose a team plays a schedule that is, overall, exactly average.

Applying it to, e.g., ASVEL Villeurbanne in the Euroleague, the equation would look as follows:

R_ASVEL = -6.90 + (1/10) * (2 * R_Cibona + 2 * R_Fenerbahce + 2* R_Montepaschi + 2 * R_Barcelona + 2 * R_Zalgiris)

A complex 24 equations with 24 unknowns. Excel will do that job for you. Now, what I like about the simple ranking system is rather not the league ranking itself – in my opinion, in Euroleague, with a limited number of games, watching games gives you a much better idea of team quality than a simple ranking – but it does commit a nice job quantifying the difficulty of the path each team has been taking to Top16. For example, it is a consesus that e.g. Olympiacos has yet to meet a Euroleague contender on its way to the Final Four, and that Prokom has had a rather easy path to the quarter finals. A look at the simple Euroleague rating system has these observations in actual numbers:

*PT MAR/G = Average point margin; OPP RAR = Average opponent rating; Team R = Team Rating by the formula presented earlier in this post*

Topping the list of weakest opponent ratings: 1. Barcelona (-2.85), 2. Olympiacos (-2.36), 3. Unicaja (-1.91), 4. ASVEL (-1.04), 5. Asseco Prokom (-1.02), 6. CSKA (-0,94)

Topping the list of highest opponent ratings: 1. Maroussi (3.60), 2. Union Olimpija (3.18), 3. Maccabi Tel Aviv (2.52), 4. Lottomatica Roma (2.13), 5. Partizan (2.08)

In simple ranking, Barcelona (by a mile) and Real Madrid top the list, third is Maccabi, followed by Montepaschi, Panathinaikos and Olympiacos. However, the point differential Olympiacos managed to reach in their games versus fairly weak competition doesn’t tell us a whole lot about their Final Four chances. Personally, I have them as the 2nd contender behind Barcelona. Partizan is another wild exception (down at #15), but the recent win in Tel Aviv showed us once again that Partizan is one of those gritty teams that never let go and whose performances are hard to put into numbers. They’re also a great reminder for everyone that statistics do have limits. According to all major ranking systems, Maccabi should still be able to win this series. We’ll see how that pans out.

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