Hey Jeff, I’m an avid Magic player, even competed on the Pro Tour and they use a form of the Elo system there. What’s neat though in their case is the K-value. The K-value is effectively the highest number of ratings points that you can win/lose in a match in this tournament.
Various types of tournaments are given different K-values which does a couple of things. Small weekly or entry-level tourneys will be 8K, larger monthly events will be 16K and qualifiers and quarterly events will be 32K.
Highly-ranked players can attend small events with much weaker players and only risk a small amount of their ratings points. Likewise, beginners tend to attend small events to start, so they only lose small chunks. Bigger tourneys allow the beginners to have “breakout” events where a good winning-streak will give you a massive ratings boost. And highly-ranked players can actually make rating points against other highly-ranked players during the big events.
The biggest limitation tends to be at the high levels of a regional ladder. If I’m ranked say 3rd in my Province/State, there may be only a dozen local people that are really “worth playing”. So I have to start going to national or Pro Tour events to meet up with evenly matched players. There are also different formats of play, so if some format of play is unpopular in your area then you can quickly end up at the top of the regional chain but nowhere in competition nationally. At some point, the better players have to attend national events and gain ratings points so that they can “bring them back” to the regional level.
They deal with bProblem #2: Decay/b by simply removing those players who are “no longer active” (the period is a little long: 1 year), but the concept is there, if you don’t play, we just dump you from the ladder. If you start playing again, you come back in at your old number.
However, I really like the concept of having a sigma and a deviation built-in to the model. Magic suffers from having Hard Ratings numbers. So if a player gets an invite for achieving a 1900 rating as of 3 weeks from now, then players have been known to not play any ranked tourneys for 3 weeks to ensure that they don’t dip below 1900 and lose their bonus.
But this is actually a failing in the difference between chess and Magic. Chess does not involve luck and Magic does. Chess players don’t have to worry about some beginner “getting lucky”; but with Magic, some days, you’re just going to lose.
And this is where some type of sigma would be nice. Even if it were some type of “momentum buffer” so that you you didn’t get raked. I’ve gone 7-1 on the day and lost rating points. I mean clearly everyone was ranked well beneath me, but even an average player can “get lucky” and beat an excellent player (which even he admitted was the case), so at some point the system should have a check for “got unlucky” or “got lucky” versus “this player is under/over-rated”.
It’s nice to know that someone has a sigma/distributed approach, I’d love to see Magic take this on.