3.2.1 How Does USATT Rating System Works?
Description
This article is from the Table Tennis (Ping Pong) FAQ, by ttennis@bu.edu with numerous contributions by others.
3.2.1 How Does USATT Rating System Works?
Before discussing the data, let's discuss how the rating system works. This
will make it easier to understand the data.
The tournament director of each tournament sends all the results for the
tournament to the USATT rating chairman Dan Simon. Dan processes the
tournaments in the order they were played. After processing, he sends a
report back to the tournament director that gives the new rating for each
player who played in the tournament. So, you may get your new rating from
the tournament director several weeks after the tournament.
Here is the rating chart which gives the number of rating points that the
winner of each match wins and the loser loses.
--------------------------------------- Rating | Higher rated | Lower rated difference | player wins | player wins --------------------------------------- 0- 12 | 8 | 8 13- 37 | 7 | 10 38- 62 | 6 | 13 63- 87 | 5 | 16 88-112 | 4 | 20 113-137 | 3 | 25 138-162 | 2 | 30 163-187 | 2 | 35 188-212 | 1 | 40 213-237 | 1 | 45 238- | 0 | 50 ---------------------------------------
However, the calculation of the ratings involves more than just this chart.
The first problem is unrated players. Dan looks at the results of each
unrated player (including the number of points the player scored). Using
this information, he assigns a rating to each unrated player. From now on
he treats unrated players just like rated players using the newly assigned
rating. So, you do win and lose points when you play an unrated player.
To finish calculating the post-tournament ratings, Dan makes two passes
through the results. The first pass is a screening pass to identify players
whose ratings should be adjusted. Dan uses the rating chart to calculate
how many points each player would win for the tournament. Any player who
would win at least fifty rating points has his rating adjusted up. This
means that Dan replaces his pre-tournament rating with a new adjusted
rating which is used as his rating for the second pass. In the second pass,
Dan uses the rating chart again to calculate the post-tournament rating for
each player.
So, from the point of view of the rating system, there are actually three
ratings for every player in a tournament. The first rating is the
pre-tournament rating which is the rating the player has going into the
tournament after all earlier tournaments have been processed. This is not
necessarily the same as the rating used at the tournament since Dan
processes the tournaments in the order they were played.
The second rating is the adjusted pre-tournament rating. This is different
from the pre-tournament rating for two classes of players:
1. unrated players,
2. players who have their ratings adjusted.
No one has a zero adjusted rating, since all the unrated players are given
a rating. If the player was rated and he is not being adjusted, then his
adjusted rating is the same as his pre-tournament rating. The third rating
is the post-tournament rating.
To summarize: the pre-tournament rating is the rating before the tournament
is processed. The adjusted rating is the rating after unrated players are
given ratings and after the first screening pass. The post-tournament
rating is the player's new rating that will be published in the next issue
of TT Today.
DATA
Dan graciously sent me the results from eight tournaments played in April
and May 1989. Here are some statistics of the number of players and matches
in those eight tournaments.
---------------------------------------------------------
Category | Players | Matches
|------------------------------------
| Number Per cent | Number Per cent
| of total | of total
---------------------------------------------------------
all | 459 100.0 | 1510 100.0
unrated | 49 10.7 | 225 14.9
adjusted | 49 10.7 | 417 27.6
unrated or adjusted | 98 21.4 | 609 40.3
---------------------------------------------------------
The row labeled "all" is all the players and all the matches. The row
labeled "unrated" is those players who were unrated going into the
tournament and those matches in which either player was unrated. The row
labeled "adjusted" is those players who had their ratings adjusted and
those matches in which either player was adjusted. The row labeled "unrated
or adjusted" is those players who were either unrated or had their ratings
adjusted and those matches in which either player was unrated or adjusted.
In case you were wondering, the number of "unrated" matches plus the number
of "adjusted" matches doesn't equal the number of "unrated or adjusted"
matches because there were 33 matches in which an unrated player played an
adjusted player. It is interesting that 40.3% of the matches involve
unrated or adjusted players. This and the fact that you don't know the
pre-tournament ratings is why you can't exactly calculate your own
post-tournament rating.
Which set of ratings should we use to construct a handicap chart? Well, in
principle we should use the pre-tournament ratings since these ratings are
closest to the ratings that are actually used at the tournaments. Rather
than make a decision, we'll construct charts using each of the three sets
of ratings.
Continue to:
My Books
