Newsgroups: rec.games.chess


Just a few questions on the USCF rating system (simplified) posted
in the chess FAQ.

Please post any answers that you may have.
Thanks.

> 
> How Ratings are Calculated: USCF Rating, Simplified
> ---------------------------------------------------
> 
> **For first 20 games, (provisional rating) use the following system:**
> 
> Take the rating of the opponent +400 if the player wins.
> Take the rating of the opponent -400 if the player loses.
> Take the rating of the opponent if the game is a draw.



If EVERYONE is UNRATED, does that mean that everyone starts from a rating
of zero (0)?  And as these people play, wouldn't some of them get a 
negative rating ?

Am I missing something?


> 
> Average these numbers.  (If unrateds play other unrateds, this requires
> several iterations of the above.)
> 

Do you mean that if every one of the player is unrated than the above 
should be iterated a few times 20 games (say 100 games)?


> **After 20 games (established rating), use the following system:**
> 
> Players rated under 2100 can win/lose a maximum of 32 points per game
> Players rated 2100-2399 can win/lose a maximum of 24 points per game
> Players rated 2400 and up can win/lose a maximum of 16 points per game
> 
> (This maximum is called the K factor.  In a 1/4 K tournament, divide
> the above numbers by 4.)
> 
> If players of equal rating play, the loser loses half of the maximum, the 
> winner gains the same amount.  No change for a draw. 
> 
> If players of unequal rating play, the higher-rated player gains fewer 
> points for a win, but loses more points for a loss.  (The lower-rated 
> player does the opposite, of course.)  A higher-rated player loses points 
> for a draw, a lower-rated player gains points.  For players rated 400 or 
> so points apart, the maximum rating change is used for an upset, and the 
> minimum gain/loss is 1 point if the much higher-rated player wins. 
> 
> The true formula for the number of points won/lost versus the ratings 
> difference is a curve, but a straight line approximation for players with 
> a K factor of 32 points can be used, where every 25 points of ratings 
> difference is one additional rating point gained/lost starting from a 
> beginning of 16 points for a win/loss, and from zero for a draw. (ie, for 
> a 100 point difference, the higher-rated player gains 16 - 4 = 12 points 
> for a win, but loses 16 + 4 = 20 points for a loss.  If a draw, the 
> higher-rated player loses 4 points, the lower-rated player gains 4.) 
> 
> The actual formula is as follows:  
> 
> K = K_Factor
> delta_R = Opponents_Rating - Players_Rating
> Expected_Wins = 1/(10^(delta_R / 400) + 1)
> New_Rating = Current_Rating + K (Actual_Wins - Expected_Wins)
> 

Should a new rating be computed for the two players the moment ONE game
is completed?

Or can they play a series of games before computing
their new ratings in bulk.


eg.  If my Expected_Wins = 0.3 and I play 2 games with my opponent and
     win both games, should my new rating be computed:


     A)   After each game
	  ---------------


     First New Rating = Old Rating  +  K ( 1 - 0.3 )

     Second New Rating = First New Rating  +  K ( 1 - not 0.3 anymore)




	  OR




      B)   After both games are completed (in bulk)
	   ------------------------------

      New Rating = Old Rating + K ( 2 - 0.6 )



      or is it



      New Rating = Old Rating + K ( 2 - 0.3 )  ???





I have been given the honor/burden of setting a chess team in the
place that I work.  To encourage more people to take part, we will
offer prizes to deserving players.  To decide who is deserving, we
have to come up with a way of rating the performance of the players
and I thought we might as well use the USCF system to make things
believable.  Yes, nobody here is rated under any chess organisation,
and none of us have the chance to play opponents with ratings - we
have to create some ratings out of nothing.


Is the FIDE rating system simpler?  It'll be good if I can see what
the difference is between the two.


Thanks in advance.


ALAN PHANG

---
Newsgroups: rec.games.chess