Monday, April 18, 2011

Introducing MLS Predictions and SRS Rankings

It's always been my goal to add analysis of the MLS to my blog.  This is a landmark season for this league.  They have expanded to 18 teams by adding newcomers Portland and Vancouver.  The Kansas City Wiz have renamed themselves Sporting KC and are opening a new stadium in June.  Real Salt Lake are playing in the CONCACAF Champions League final this month, trying to become the first MLS team to win this tournament. 

The season kicked off on March 15 and with every team having played at least four matches, I now have enough data to make match-day predictions and calculate meaningful SRS rankings.  However, I'm not able to make season projections yet.  Sporting KC's new stadium will not open until June 9th so they are playing nothing but road matches until that time.  I won't be able to project their home performance until they play a few home matches so won't be able to project their full season performance.  The way their schedule is laid out they play 11 of their first 12 MLS matches on the road.  The MLS makes it up to them by scheduling them to play 11 of 12 home matches during a stretch from July through September.  By mid-June I will have enough home data for Sporting to project the entire season for the MLS.

In the meantime I will still make predictions for upcoming matches.  Here are my picks for this week's games with the home team listed first:

DC United 2  New York 1
Colorado 4  Seattle 1
San Jose 0  Chivas USA 0
Toronto FC 1  Columbus 0
Vancouver 3  FC Dallas 2
New England 2  Sporting KC 2
Chicago 1  Houston 2
Real Salt Lake 2  Philadelphia 0
Los Angeles 2  Portland 0

I will post my first SRS rankings for the MLS after the jump.

SRS stands for Simple Ranking System which is a widely used method for ranking teams in sports leagues.  A detailed description of this method can be found here.  Basically this method ranks teams by margin of victory (MOV) adjusted for their strength of schedule (SOS) which is equivalent to their opponents' average margin of victory.  SRS = MOV + SOS.  If a team plays mostly weak opposition their SOS tends to be negative indicating that their MOV is inflated.  A team that plays a tough schedule will have a positive SOS indicating that they are stronger than what their MOV indicates.

Here are the SRS rankings for the MLS based on matches played as of 4/17:

Real Salt Lake1.7500.2502.000
New York0.6000.2500.850
D.C. United0.200-0.0200.180
Los Angeles0.0000.1190.119
New England-0.3330.328-0.006
San Jose-0.4000.240-0.160
Chivas USA-0.400-0.193-0.593
Kansas City-0.250-0.363-0.613
FC Dallas-0.400-0.250-0.650
Toronto FC-0.500-0.308-0.808

The color coding indicates which team is the best (Green) and worst (Red) in each category.  This data is based on a small number of matches for each team so these results can change quite a bit from week to week.  Over the course of a long season, they will stabilize and we will start to get the true measure of each team.  

These results are based on all MLS matches (home and away) and do not include CONCACAF or US Cup matches.  What this table shows above is that Real Salt Lake (RSL) has performed the best by far this season.  Their average margin of victory is 1.75 goals per game.  Their opponents' combined margin of victory is 0.25 goals per game which results in an SRS of 2.00 goals per game.  In other words if RSL played an average team (0.00 MOV) with an average schedule (0.00 SOS), they would be expected to win by 2 goals.

At the opposite end of the spectrum is my home-town team, the Chicago Fire.  They have been outscored by 0.6 goals/game by opponents that themselves are outscored by 0.363 goals per game.  So they are losing to losing teams which hurts their SRS rating.


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