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 Post subject: Re: Revised European go ratings
Post #101 Posted: Sat Nov 11, 2017 1:48 am 
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Rank: EGF 3d
KGS: gennan
Uberdude wrote:
gennan wrote:
Also, I don't think various national lists exist (I know only of France and Belgium). As far as I know, most countries just use the European list.

In Britain we use the European rating system, but we used to apply a linear transform to convert an EGF rating to a British dan/kyu rank. We would look at the average rating of a player declared as a 1 dan in Europe (it was a bit less than the theoretical 2100) and also the average rating gap between declared ranks (not sure exactly over what range, it was a bit less than the theoretical 100) and then apply extrapolate these, e.g. 1 dan is 2070 and 95 points per rank so 3 dan is 2070 + 2*95 = 2260 rather than 2300. However, this adjustment was abandoned earlier this year.

Interesting. So the BGA detected this issue: http://goratings.eu/Histograms/Histogram_EGD?year=2012&country=UK and used a transformation to get something like http://goratings.eu/Histograms/Histogram_Revised?year=2012&country=UK. It's a nice workaround, but I think it's preferrable to improve the source system instead, so that workarounds like this are not needed.

BTW, I think the required 95 points per ranks is a sign of the contraction effect caused by the unrealisitic winrate predictions of the EGD. I think that without rank resets, handicap games and new player ranks countering this contraction, over time the EGD ranks spacing would tend to shrink to about 50 points per rank (except for high dans). See http://goratings.eu/Probabilities which determines the spacing between ranks from even game winrates.

I used the revised rank spacing in the scaling of the vertical axis of my player rating histories, for example http://goratings.eu/Home/History?PIN=10449472.


Last edited by gennan on Sat Nov 11, 2017 11:29 am, edited 1 time in total.
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 Post subject: Re: Revised European go ratings
Post #102 Posted: Sat Nov 11, 2017 2:16 am 
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Was liked: 11
Rank: EGF 3d
KGS: gennan
WinDigo wrote:
gennan wrote:
Also, I don't think various national lists exist (I know only of France and Belgium). As far as I know, most countries just use the European list.

Ukraine also has its own ranking system. As far as I know, there are three major differences from EGF ratings:
  1. Dropping for more than 100 points is allowed.
  2. After-tournament ratings are calculated sequentially, i.e. ratings "change" during the tournament. However, this doesn't affect seedings.
  3. There is a term "abnormal tournament result". If player performed in tournament far better than his(her) rating, then he(she) gets a new one (the result of calculation) and the whole tournament is recalculated. This protects other players from losing too many points. Also, the "abnormality threshold" is different for every initial rating.

Thanks for your info!

1. I can understand that the 100 point drop limit helps the EGD against deflation, because in combination with the large K factor that the EGD uses for lower ranks, it basically inflates lower ranks (in a somewhat convoluted way). The revised system also allows dropping more than 100 points, but because of the smaller K factor for lower ranks in the revised system, it hardly matters (even lower ranks don't drop 100 points that often in the revised system). But it just seemed like a very arbitrary rule to me, so I left it out of the revised system, like in the Ukrainian system.

2. Currently, the revised system also updates the participant rating sequentially for each game in a tournament. But it only does that while processing the games for each participant separately. For their opponents, it uses the pre-tournament rating. But perhaps I'll change this procedure a bit (see point 3).

3. That sounds very similar to the French system: iterating to fix anomalies. This is not how standard Elo systems work. It introduces an element of systems like Glicko or Rémi Coulom's WRH system. It's interesting and I have no problem with deviating more from Elo, but it does feel a bit arbitrary to me to distinguish between normal and abnormal results. I feel that it should be a smooth transition and not some threshold that triggers a different algorithm for a few participants.
Perhaps this can be achieved by updating each participant's K factor from the likelyhood of their results when processing a tournament. Also, a resulting increase from the normal K factor could be used to reduce their opponents rating changes in a post processing step. This would be similar to the rating reset mechanism currently used by the revised system.

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