Hi, I'm working at a chess club for a local elementary school, and I wanted to implement a Lichess like rating system using Glicko-2. Ussually in this club kids will play about 1 game a week during the club.
I would like to make the ratings update after each game, just like it does here on lichess, how do I make that work without running into problems with having the rating periods be to short? How does Lichess handle this issue?
This was actually only recently fixed on lichess. The solution is to allow fractional rating periods (currently lichess says a rating period is 4.6 days which is kind of arbitrary but is tuned for our purposes, you can probably have it be longer).
Then after each game, the only change is in the new rd calculation. Instead of sqrt(phi2 + sigma2), you use sqrt(phi2 + t × sigma2), where t is the number of rating periods since the last rd update (which might be less than 1 for consecutive games or more than 1 if you haven't played in a while).
github.com/ornicar/lila/blob/e5c8f7ddcdafa7ce6d3303b0de3035a4eb0693a0/modules/rating/src/main/java/glicko2/RatingCalculator.java#L316So if I play you in a game, lichess will show me an adjusted rating after we finish the game, what is going on with that if it only does rating periods every 4.6 days?
Sorry, I'm probably being a bit unclear about the terminology. I meant that we calculate new ratings immediately after every game, with the formula change I mentioned above. 4.6 days means that if you play a game after 2 days, you calculate t = 2/4.6 = 0.435 and use that in the formula.
I can go into more detail if you want, but what I'll recommend to you is that you don't worry about it - if everyone's only playing 1 game a week, you can do a normal one-game Glicko rating period after every game. It won't be perfect, but to compare to lichess, we have to handle some players with hundreds of games a week so we had to do more work to account for that.
Great, that makes a lot of sense. I really appreciate you explaining this all to me.
The Chess Ranking Assistant, a free Excel add-in, does Gkicko ratings. I originally created it for my grand sons’ school chess club. It since has been greatly enhanced. It works only on PCs.
To download, go to
www.add-ins.com/free-products/chess-ranking-assistant.htmTo see a posting of its output, see
http://www.tristatechess.club/chess-ladder.htmlI printout the win loss worksheet and tape together and take to the club. The same works fine for school clubs. No need to post on the Internet