Forum Archive : Ratings

Ratings variation

From:   Kevin Bastian
Address:   kbastia@ibm.net
Date:   14 February 1999
Subject:   Re: FIBS:Keeping the rankings credible
Forum:   rec.games.backgammon
Google:   01be57e0$c3155ac0$11c86420@kbastian

Hi folks. Long time, no see. Haven't been here for awhile. Got tired of
sifting through the 90% of the posts dealing with whether or not FIBS,
Jellyfish, etc. cheat or not :-)

As for ratings, thought I'd share some data with you. I started logging my
FIBS matches a year ago, inspired in part by my old buddy (and nemesis!)

Having been a spreadsheet junkie/guru for...hmmm...18 years or so (yikes!),
I've been logging them in an Excel spreadsheet. Have quite an array of
linked graphs and such. The other night, someone asked my opponent and me
how much ratings seem to vary from one's "true" rating, so I checked my
spreadsheet. Added a few lines to check the mean, median, max, min,
standard deviation.

For what it's worth, if it adds to the discussion any, here is the data:

2/27/98-2/13/99 KevinB on FIBS:

1150 matches
4911 experience
4.27 average match length
1658.55 minimum
1792.08 maximum
1724.50 median
1725.82 mean
24.25 standard deviation
18.98 average deviation
70% of the time my rating was within 1 std. deviation of the mean
94% of the time it was within 2 std. deviations
100% of the time it was within 3 (the max was 2.73 std. dev above the mean;
the min was 2.77 below mean)

What does all this mean? Well, first of all, I'm sure many of you know far
far far more than I about statistics, so you tell me! But I will offer some

First, a bit of background. I've played 21,919 experience on FIBS over the
past 4 years. I'm a "serious" player; i.e., I don't play 99 point matches
that are over in one game, etc. I play nearly all my matches with opponents
who are between 1600 and 1900. I wish I'd logged the ratings of my
opponents at the time of the matches, but I didn't. Generally, I look at
the ready list and invite the highest rated player who meets several
criteria: not a cheater (or a jerk), 1000+ experience, ideally if I've
played them before and know they move quickly, aren't unpleasant, etc.
Anyway, I start at the top. So, I'd guess that the average rating of my
opponents is higher than mine by 25 pts or so, but just guessing.

The other thing is that I'm (unfortunately) pretty well past my learning
curve in this game. The first several years on here, I improved a lot, but
since then, I've been pretty stable. So, I think the above data is a pretty
good indication of what a "stable" (not learning & improving a lot) player

I have had some long term upswings and downswings over the past year. I do
NOT attribute them to luck. I'm sure a bit of it might have been luck, but
I don't think much of it was. One of the graphs my spreadsheet system
automatically produces for me is a semi-monthly bar graph of how much I
play. My interest and available time have varied over the past year, and I
found that when I got really psyched about backgammon, and was determined
to get my rating up, two things ALWAYS happened: I played a lot more. My
rating went up. Then, I'd start to lose interest. I'd play less. My rating
would go down. Recently, I got a bit down in the dumps for a few days. Had
trouble being very interested in much of anything. So I played a lot of
FIBS, although I wasn't highly focused. I lost 10 out of 11 matches. And I
was NOT swearing at the dice! For the most part, I was pretty sure I just
wasn't playing that well. After a couple days of that, I woke up feeling
much better. Had my head sorted out I guess. And one of the things I
decided to do was win back my points. I immediately won 10 of my next 11
matches, and was right back where I started from before the slump. Talk
about mind over matter! Now, this may have been accompanied by a bit of bad
luck on the downslope and good luck on the upslope, but by and large, it
was mood, focus, concentration, etc. Certainly, these will be swing more
with some people than others.

Anyway, what my data shows for me, at least over the past year, is that I
spend roughly 95% of the time within +/- 50 points of my "true" FIBS rating
of 1725.

Kevin Bastian
KevinB on FIBS

Tom Keith  writes:

Douglas Zare and Adam Stocks comment on this posting in their article
"Ratings: A Mathematical Study"
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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