Is Glicko biased?

[flovo]

Sorry for the short answer. Somewhere on the forum are lengthy explanations how the rating system works.

The rating system is not biased in one direction. If it would be the case, OGS would have a big problem with rank deflation.
Rating changes are calculated using

• your rating, deviation and volatility at the begin of a rating period (volatility is not shown on OGS)
• the current rating and deviations of all of your opponents in that rating period
• the info if you won/lost the games.

A rating period consitsts of up to 15 games.

The rating change is antisymmetric in rating difference (losing against a 100 points weaker opponent = - winning against a 100 points stronger opponent)

Neither reason for win/lose nor the score have any impact on rating changes

@AdamR

My rank decreased after a win / My rank is behaving weird

Long story short - the rank calculation is a complicated process our developers spent a long time on. It may be doing something strange at first sight , but we are pretty confident it is working more or less correctly.

The main source of confusion is that the ranking system is constantly recalculating your rank based on how the rank of your past opponent changed (to the extend of last 15 games). This is a good thing! But it may in certain circumstances even lower your rank after you have won another game (you always get the points for the win, but some of the points you have gotten previously can be decreased).

Say you have played a 5 stones stronger player in the recent past and beat him. You get a lot of points for that, it is after all a big acomplishment. But later this player’s rank fell a lot. That probably means the player was not on the level the system thought and the boost to your own rating might have been too much. Therefore some of the points given to you for that victory can be decreased retroactively. It may feel disappointing at first, but it helps a lot to get the most precise estimate of your actual rank.

There is more about the rating system

OGS has a new Glicko-2 based rating system! [2017]

tl;dr We’re switching to a Glicko-2 rating system, which should be great for a lot of reasons. All of your past ranked games have been accounted for during this transition. Hello OGS! For the past several years we’ve been using a rating and ranking system based on Elo developed by the European Go Federation. It has served us reasonably well, but there have been some shortcomings when applying that system in an online setting. Most of the shortcomings can be traced back to the fact that the sy…

And the math of glicko
http://glicko.net/glicko/glicko2.pdf