Home » Forum Home » Help

Topic: Rating problem ?
Replies: 2   Views: 14,135   Pages: 1   Last Post: Jan 3, 2005, 11:35 PM by: dweebo

Search Forum

Back to Topic List Topics: [ Previous | Next ]
Replies: 2   Views: 14,135   Pages: 1  
nosovs

Posts: 205
Registered: Dec 16, 2001
From: Moscow,Russia
Age: 56
Home page
Rating problem ?
Posted: Dec 30, 2004, 12:11 PM

* game over, nosovs wins *
* nosovs's rating has gone from 2162 to 2151. *
* markpsinas's rating has gone from 1570 to 1581. *
nosovs: I don't understand why my rating fall down ?

I can not understand why rating fall down if I won ?



up2ng

Posts: 542
Registered: May 9, 2002
From: Northeast USA
Age: 38
Re: Rating problem ?
Posted: Dec 30, 2004, 9:07 PM

nosovs,

Yes, you have experienced what some consider to be a minor flaw in the DSG rating system. Specifically, the flaw exists only in the provisional rating system. Also, it tends to only happen to those players with an exceptionally high rating while still in "provisional" status.

This flaw is explained in more detail in other ratings related forum posts. For other explanations, visit the following links starting from the main page at DSG:

(Documentation section) FAQs -> General FAQ -> ...
"How are the ratings calculated?"
"What does provisional mean?"
"I won but my ratings went down!?!?"

I'll try to expand on the explanation of the provisional formula as I understand it.

When you complete a game, a "value" is generated as follows:

value = (r1 + r2) / 2 + w * 200 + e * 200
where:
r1 is your rating before the game
r2 is your opponent's rating before the game
w = -1 if you lost, w = 1 if you won
e = 0 if your opponent is established, e = w if your opponent is provisional.

Notice that if you are rated more than 400 points higher than your opponent (and in some cases, more than 800 points higher) this "value" will be smaller than your initial rating even if you won.

What is not explained above, but what I believe happens, is that this "value" is then factored into your new rating as a "weighted average" against your previously generated "values". For example, this was your 9th game, so you already had 8 "values" whose average was 2162. Using the formula, your 9th value is:

(2162 + 1570)/2 + 200 + 0
= 1866 + 200
= 2066

I believe this gets factored in to your new rating as follows:

new rating = ((2162 * 8) + 2066) / 9
= (17296 + 2066) / 9
= 19362 / 9
= 2151.333 (there are decimal points behind the scenes)

The only point I'd like to make to Dweebo here is that your opponent was actually provisional, which, according to the description in the FAQ, should have given you a value using e = w = 1 instead of e = 0, which would have caused your rating to go up in this case (since you were NOT 800 points higher than your provisional opponent). It is possible that the description for e in the FAQ is reversed or otherwise incorrect.

There are a few conclusions to make here. First, you are still in "provisional" status, which means you have not played enough games for the computer to calculate an "accurate" rating for you yet. This is defined to occur after 20 rated games, when you begin using the "established" formula. In the established formula, it is impossible for your rating to go down when you win. The purpose of your provisional games is to "zero in on" a reasonable estimation of your rating by the time you become established. Do not get too hung up on what your actual rating is during this time, as it can change dramatically during the course of playing only a few games.

If losing points when you win is still unacceptable to you, the easy solution is to try to play against opponents that have a rating close to yours (within 400 points). If no one is available with a high enough rating, feel free to play unrated games. But PLEASE, do not avoid playing at all because of this minor flaw, we want to encourage more playing, not less!!

Finally, nosovs, I know that you are an extremely good player. Unlike some players that have tried to abuse the simplicity of the provisional rating system, I know that you deserve the high rating that you have attained so far. PLEASE, do not be discouraged by this incident. I am very happy to see you playing games here at DSG, and hope very much that you will continue playing many more real time games!

Hope that helps! Look forward to playing pente against you soon!

dweebo

Posts: 1,031
Registered: Dec 16, 2001
From: Powell, OH
Age: 37
Home page
Re: Rating problem ?
Posted: Jan 3, 2005, 11:35 PM

I think up2ng got it all right, though I didn't read it that closely, this issue was discussed at LENGTH earlier and is in the forums if you search for it. I remember at the time being satisfied with the conclusion of everyone's combined analysis as to what ACTUALLY happens, so I'm not revisiting it right now.

I should update the FAQs if they are incorrect though.
-dweebo

Pente Rocks!
Replies: 2   Views: 14,135   Pages: 1  
Back to Topic List
Topics: [ Previous | Next ]


Powered by Jive Software