Forum Archive : Ratings

Table of ratings changes

From:   Patti Beadles
Address:   pattib@netcom.com
Date:   22 August 1994
Subject:   Re: FIBS ratings formula
Forum:   rec.games.backgammon
Google:   pattibCuwttn.F8v@netcom.com

Ratings changes are based on several things-- the length of the match,
the experience level of each player, the current rating of both
players, and whether the higher-rated or lower-rated player wins.

Experience figures into this in an interesting way.  For players with
400 or more experience points, there's no influence.  For players with
less than 400, the experience turns into a simple multiplier.  Your
experience affects your rating change only, not that of your opponent.

Here are a couple of tables showing the ratings change for various
match lengths and ratings differences.  Note that you need to use a
different table depending upon whether the higher-rated or lower-rated
player wins.

       Ratings change when higher-rated player wins,
       assuming 400+ experience.*

diff         1         3         5         7         9        11
----     --------  --------  --------  --------  --------  --------
100      1.884998  3.119854  3.899648  4.491772  4.974016  5.381994
200      1.770753  2.782339  3.345620  3.727760  4.006327  4.216725
300      1.658005  2.457773  2.826207  3.029076  3.142692  3.201313
400      1.547453  2.151421  2.353534  2.415209  2.409120  2.366478

       Ratings change when lower-rated player wins,
       assuming 400+ experience.*

diff         1         3         5         7         9        11
----     --------  --------  --------  --------  --------  --------
100      2.115002  3.808349  5.044624  6.091233  7.025984  7.884505
200      2.229247  4.145864  5.598652  6.855246  7.993673  9.049774
300      2.341995  4.470430  6.118065  7.553929  8.857308 10.065186
400      2.452547  4.776783  6.590738  8.167797  9.590880 10.900022

* For a player with lesser experience, multiply the number in the
table by -experience/100+5, e.g. for 200 experience, 3.

So if a 1500 player beats a 1700 player in a 3-point match, I would
look in the table and find that for a 3-point match, lower player
wins, 200 difference, the change is 4.15 (rounded.)  If the 1700
player won, the change for both players is 2.78.

Did you find the information in this article useful?          

Do you have any comments you'd like to add?     



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Ratings variation  (Kevin Bastian+, Feb 1999) 
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Table of ratings changes  (Patti Beadles, Aug 1994) 
Table of win rates  (William C. Bitting, Aug 1995) 
Unbounded rating theorem  (David desJardins+, Dec 1998) 
What are rating points?  (Lou Poppler, Apr 1995) 
Why high ratings for one-point matches?  (David Montgomery, Sept 1995) 

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