Forum Archive :
Here is a cut and paste from GamesGrid's description of their rating
system. Hopefully this answers some of your questions.
From GamesGrid webpage:
"How are ratings calculated? What do they mean?
The ratings system is designed to yield stable ratings that accurately
reflect the relative abilities of the players.
Each player begins with a rating of 1500. Ratings are increased or
decreased when a player wins or loses rated matches. The ratings change for
each match is based on the length of the match and the ratings difference
between the players. The longer the match, the more ratings points are
Since the higher-rated player is more likely to win a match, especially as
the match length increases, a lower-rated player gets favorable odds when
playing a higher-rated player. For example, suppose a player rated 1550
challenges a player rated 1850 to a 7-point match. The player rated 1550
stands to gain 7.7 rating points if he wins, and lose only 2.9 rating
points if the higher-rated player wins. Conversely, The player rated 1850
stands to gain only 2.9 rating points if she wins, but lose 7.7 rating
points if the lower-rated player wins.
These numbers reflect the match winning chances (MWC) for each player,
based on the difference in rating and length of the match. (In the example,
the lower-rated player has approximately 27% MWC, and the higher-rated
player 73% MWC). The win/lose numbers are shown in the invitation dialogue.
There is an initial adjustment period of 500 games (called "the ramp").
During this period, your rating will change more rapidly, in order to more
quickly adjust to an appropriate level. Using the same example as above, if
the lower-rated player had only 5 experience points, he would stand to gain
30.8 rating points if he wins, and lose 11.5 rating points if he loses.
(The risks for the higher-rated player remain the same, assuming more than
500 experience points.) As your experience approaches 500 games, the rate
of change decreases to the standard rate.
Do I get more ratings change if I win by more points?
The amount of ratings change is based on the length of the match and the
difference in ratings between the players. There is no bonus for winning
more points than are necessary to win the match. For example, in a 7 point
match, winning 1024-0 has the same ratings impact as winning 7-6. In
particular, there is no benefit to winning a gammon if a simple win gives
you the match. You win the match either way, and allow your opponent to save
time and face.
For this reason, experienced players will offer a simple resignation in a
hopeless position, when the current cube value is sufficient to give their
opponent the match. Their opponent should accept it, and record the win,
even if a gammon is possible. While they are within their rights to play
the game out, there is no ratings benefit to wasting the time. They should
accept their match victory graciously, and move on to the next match.
Why do some players start higher than 1500?
GamesGrid offers players who have proven their backgammon skill in other
venues the opportunity to start above 1500. This helps those players get
matches at a competitive level. Also, it is fairer to their opponents, who
would give up substantial equity by playing a high-rated player at 1500 just
because they are new to GamesGrid.
In order to start at a higher rating, an account must be a newly created on
GamesGrid (no experience points) with a minimum membership commitment of 6
months. Transfer of membership from another GamesGrid account for this
purpose is not permitted.
We currently recognize the following equivalencies for players from other
Winners of major international tournaments may start at 1800. The maximum
rating transferred is 1800, with a minimum membership investment of six
months from date of transfer.
The equivalencies may change from time to time, and we reserve the right to
modify the formulae at any time in order to maintain the fairness of the
End of quote.
Zox at GamesGrid, Zone
- Constructing a ratings system (Matti Rinta-Nikkola, Dec 1998)
- Converting to points-per-game (David Montgomery, Aug 1998)
- Cube error rates (Joe Russell+, July 2009)
- Different length matches (Jim Williams+, Oct 1998)
- Different length matches (Tom Keith, May 1998)
- 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)
- Fastest way to improve your rating (Backgammon Man+, May 2004)
- Field size and ratings spread (Daniel Murphy+, June 2000)
- Improving the rating system (Matti Rinta-Nikkola, Nov 2000)
- KG rating list (Daniel Murphy, Feb 2006)
- 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)
- Ratings and rankings (Chuck Bower, Dec 1997)
- 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)