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FIBS Rating Variation #1

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Aug 13, 1997, 3:00:00 AM8/13/97

The idle brain being the devil's tool, I decided to explore the amount of
random varatiation in FIBS ratings.

I built a model with the following parameters:

1. An individual has a given "true" rating.
2. The FIBS rating formula accurately describes this player's likelihood
of winning a match vs. other players, based on their ratings.
3. Player plays only 5-point matches, against opponents who randomly have
ratings of 1500, 1600, 1700, 1800, or 1900.
4. Ratings were set assuming experience >400.

I'm running a number of tests on it. The one I've done so far concerns a
player with a "true" rating of 1800, who starts at 1800. The question is,
if (s)he plays, how high or low will the rating go.

I found that, based on the following number of matches, the AVERAGE
maximum and minimum ratings achieved were:

1000 1881 / 1719
2500 1902 / 1698
5000 1916 / 1682
10000 1929 / 1668

This suggests that for players who play a lot, rating variations of 200
from high to low are not surprising, or alternatively, variations of 100
to 125 from their "true" rating.

In all cases, I am simulating at least 10,000 player histories, sometimes
more. In other words, I am simulating tens of millions, up to billions,
of matches. The standard error of my results is likely to be quite small.

I'm going to use the model to run some other tests, and I'll bore the
newsgroup with the results.

- Hank (Hank_VaUSA)

Patti Beadles

Aug 13, 1997, 3:00:00 AM8/13/97

A couple of years Ed Rybak did exactly the same thing, and got the
same results. I've always used +/- 100 points as an expected ratings

Patti Beadles | | | "I trust you. It's just
or just yell, "Hey, Patti!" | that I'm scared of you."


Aug 13, 1997, 3:00:00 AM8/13/97

Does anyone know how the ratings affect the rankings on FIBS? What I
mean, is how often are the rankings "refreshed" after ratings changes
after completed matches? For example, playerA goes into a match with a
Rating of 1600.01 and Ranking of 1336, wins, and moves up to a Rating of
1610.08 and Ranking of 1287. If playerA checks his/her rating
immediately after the match using the ratings command, it will return a
ranking of 1287 and a rating of 1610.08. But if s/he checks the ranking
again, say , an hour later, without having played any matches, the
ranking will be the same 1287. With matches being played all the time
on FIBS, with other players' ratings increasing and decreasing
(sometimes by a lot), shouldn't this cause playerA's ranking to be
different than when s/he last checked it? Wouldn't it have probably
gone up or down a bit?

Of course, this could all be moot if the rankings do indeed presently
reflect the actual ratings rankings, and maybe the reason why playerA's
ranking hasn't changed is because out of the thousands of players who
have id's and ratings rankings on FIBS there just weren't any of them
recently playing who won/lost to cause playerA to move up or down in the

Patti Beadles

Aug 14, 1997, 3:00:00 AM8/14/97

The rankings are updated instantaneously. If you're, say, #1287, do
"rat from 1280 to 1295" to see the people around you.
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