Forum Archive : Ratings

On different sites

From:   Bob Newell
Address:   bnewell@linux.chungkuo.org
Date:   5 April 2004
Subject:   Rating comparisons
Forum:   rec.games.backgammon
Google:   slrnc73roa.mtn.bnewell@linux.chungkuo.org

How do ratings compare from site to site?

Douglas Zare  writes:

For a while, GamesGrid and FIBS were about equal. I'm
pretty sure that FIBS has weakened while the GamesGrid
ratings have dropped, at least at the top, but the gap isn't
close to 300 points. Keep in mind that there are players on
both sites who manipulate their ratings, there are separate
populations of players within the servers whose ratings
are not comparable, and that individual ratings may
have standard deviations of over 50 points through normal
swings of the dice.

Here are a few examples of ratings for players who have
recently played on both sites:

1850 (GG), 1897 (FIBS), +47
1893 (GG), 1979 (FIBS), +87
1911 (GG), 1921 (FIBS), +10
1905 (GG), 1917 (FIBS), +12

It could be that things are different at lower ratings, but
I doubt it. There are fewer than 50 out of 3000 players
on GamesGrid rated under 1300.

Douglas Zare

happyjuggler  writes:

I am only familiar with 4 rating systems.

First, The "Zone"'s rating system is hopelessly flawed for several
reasons but the main ones are  that most of the other flaws draw from
is that it rounds off to the nearest integer. The other one is that
players can "play" matches vs themselves via using 2 pc's and the Zone
does not seem to give a fig. Thus anyone within +/- 400 points (I
believe the cutoff is actually around 440 but it has been a long time
since I played in their rated rooms) who plays a 1pt match both gains
and loses the same amount of points (2). Subtract anywhere from 0pts
to about 4000pts (not a typo) to get an accurate comparison of Zone
ratings with the following 3 systems.

The next 3 rating systems are all based (more or less...with an
emphasis on more) on the same rating system.

GammonZone (GZ). Free. This is probably the rating System I play in
the most at the moment. This is entirely tournament based. There are
daily tournaments of 3pts or 7pts (3pts are more common unfortunately
imo...but give the people what they want). Each month they have 2
playoff tournaments (tpts each...one is double elimination) based on
results from the daily play. They also have a round robin league with
several bracket and divisions with 21pt playoffs. They also run a
monthly tournament called Medallion which is mostly 11pts with 13 or
15 for the final rounds. Progressive Consolation for Medallion is also
11pts. Second chance Medallion is 9pts but anyone can enter with
preference given to players who lost in Medallion that month(I believe
the cutoff for 2nd Chance is 128 players). They also run a couple of
tough tournaments a year (lasting 3-4 months) that are basically best
3 of 5 11pt series in a single elimination format (13 and 15 pts for
the later rounds) and the consolation has a "crazy" match length of
something like 17pts early rounds to 29pts later rounds.

GZ's rating system is sound and rating updates are posted weekly. The
strength of the tournaments varies wildly with the longer ones tending
to draw much stronger players.

GamesGrid (GG). Pay site. GG is a site that runs some small
tournaments (mostly 1pters) but is mostly pick your opponent. A lot of
the world's best players play there (e.g. Woolsey, Robertie). They
have guest memberships that are free but are not available for ratings
or money accounts. Those with a full membership play their choice of
rated or unrated matches of money sessions. You can play for money if
you have a money account but you don't need a money account to play.
There are bots available to play (for members only). GG has a "saved
match" system that is adjudicated by Snowie after a couple of weeks if
the players do not resume play and GG keeps track of a players
completion percentage on the player info page.

GG's rating system is mostly sound but many players are deliberately
underrated so as to better entice others to play with them for money.

FIBS. Free. FIBS is almost entirely a pickup match system with no
daily tournament I am aware of and a very small number of website
based tournaments that take a few months or so to play. Getting
started the first time is a pain in the butt but once you get there it
is worth it for the most part. There are many different interfaces to
use but I have only tried 3DFIBS and love it. There are bots available
to play. They have a "saved match" system designed to allow you to
replay unfinished matches due to booting but some players abuse it and
quit instead of allowing the rating system to knock off points for
losses. Fortunately you can view the players' "saved" games numbers
and simply not play those with lousy ratios to matches played.

FIBS seems mostly sound but I am not sure I have figured out all the
"angles" that players may use to abuse artifically inflate their

When I played on GG my ratin was about 1830 when I stopped and had a
high rating of about 1910. This is with about 5000 or so experience
points if memory serves. My GZ rating is officailly about 1830 but I
had a good week so far and it will probably be about 1860 on Sunday
when the list is updated assuming I don't play more and have it go up
or down more. My high GZ rating is 1945. This is with about 5000
experience points. I am currently in a "down" period for my rating and
I think (perhaps very wrongly) that is "belongs" somewhere around
1900. My FIBS rating is about 1800 with a high about 1830 and
experience points of about 800. I do not think my rating is high
enough for my relative strength there yet but this is obviously
subjective assessment.

The problem with cross-platform rating comparisons is that you need a
huge body of players who play in each of the different systems to be
able to call the systems numbers compatible but I believe my numbers
are roughly normal for a player on the relatively high end and Douglas
Zare's examples ring true based on what I have personally experienced.
Did you find the information in this article useful?          

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



Constructing a ratings system  (Matti Rinta-Nikkola, Dec 1998) 
Converting to points-per-game  (David Montgomery, Aug 1998)  [Recommended reading]
Cube error rates  (Joe Russell+, July 2009)  [Long message]
Different length matches  (Jim Williams+, Oct 1998) 
Different length matches  (Tom Keith, May 1998)  [Recommended reading]
ELO system  (seeker, Nov 1995) 
Effect of droppers on ratings  (Gary Wong+, Feb 1998) 
Emperical analysis  (Gary Wong, Oct 1998) 
Error rates  (David Levy, July 2009) 
Experience required for accurate rating  (Jon Brown+, Nov 2002) 
FIBS rating distribution  (Gary Wong, Nov 2000) 
FIBS rating formula  (Patti Beadles, Dec 2003) 
FIBS vs. GamesGrid ratings  (Raccoon+, Mar 2006)  [GammOnLine forum]
Fastest way to improve your rating  (Backgammon Man+, May 2004) 
Field size and ratings spread  (Daniel Murphy+, June 2000)  [Long message]
Improving the rating system  (Matti Rinta-Nikkola, Nov 2000)  [Long message]
KG rating list  (Daniel Murphy, Feb 2006)  [GammOnLine forum]
KG rating list  (Tapio Palmroth, Oct 2002) 
MSN Zone ratings flaw  (Hank Youngerman, May 2004) 
No limit to ratings  (David desJardins+, Dec 1998) 
On different sites  (Bob Newell+, Apr 2004) 
Opponent's strength  (William Hill+, Apr 1998) 
Possible adjustments  (Christopher Yep+, Oct 1998) 
Rating versus error rate  (Douglas Zare, July 2006)  [GammOnLine forum]
Ratings and rankings  (Chuck Bower, Dec 1997)  [Long message]
Ratings and rankings  (Jim Wallace, Nov 1997) 
Ratings on Gamesgrid  (Gregg Cattanach, Dec 2001) 
Ratings variation  (Kevin Bastian+, Feb 1999) 
Ratings variation  (FLMaster39+, Aug 1997) 
Ratings variation  (Ed Rybak+, Sept 1994) 
Strange behavior with large rating difference  (Ron Karr, May 1996) 
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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