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Before an event, a player is either unrated, or has a rating
based on having played games.
A player's rating is termed ``provisional'' if it is based
on 25 or fewer games, and is ``established'' otherwise.
Assume the player competes in games during the event.
Post-event ratings are computed in a sequence of five steps:
- The first step sets temporary initial ratings for unrated players.
- The second step calculates an ``effective'' number of games
played by each player.
- The third step calculates temporary estimates of ratings for
unrated players only to be used when rating their opponents on
the subsequent step.
- The fourth step then calculates intermediate ratings for all players.
- The fifth step uses these intermediate ratings from
the previous step as estimates of opponents' strengths to
calculate final post-event ratings.
The calculations are carried out in the following manner:
- Step 1:
- Set initial ratings for unrated players.
Initial rating estimates are set for all unrated players in an event.
The purpose of setting initial rating estimates for unrated
players is (1) to be able to incorporate information about a
game result against an unrated player, and
(2) to choose among
equally plausible ratings during a rating calculation for an
unrated player (see the details of the ``special'' rating formulas
in Section 2.2.
An initial rating for an unrated player is determined in the
following order of precedence.
- If an unrated player has a FIDE rating,
use a converted rating according to the following formula:
If the FIDE rating is over 2150, then
this converted rating is
treated as based on having played 10 games ().
If the FIDE rating is 2150 or less, then
this converted rating is
treated as based on having played 5 games ().
- If an unrated player has a CFC rating over 1500,
use a converted rating according to the following formula:
This converted rating is
treated as based on having played 5 games ().
If an unrated player has a CFC rating of 1500 or less,
use a converted rating according to the following formula:
This converted rating is
treated as based on having played 0 games ().
- If the event is a regular event and the player has a
QC rating (and does not have a standard rating)
based on at least four games,
use the QC rating as the imputed standard rating.
The rating is assumed to be based on 0 games
().
Conversely, if the event is a QC event and the
player only has a standard rating based on at least four
games, use the standard rating as the imputed rating.
The rating is assumed to be based on the lesser of 10 and
the number of games upon which the standard rating is based
( or number of prior QC games, whichever is smaller).
- Otherwise, impute an age-based rating according to the
following procedure.
Define a player's age (in years) to be
The formula for an initial rating based on age is given by
The rating is assumed to be based on 0 games ().
As a practical concern, if ``Age'' is calculated
to be less than 4 years old, then it is assumed that a miscoding
of the player's birthday occurred, so that such a player is
treated as a 20-year old in the Age-based calculation.
- If no international rating or birth information is
supplied, and if the player does not have a non-correspondence
USCF rating, impute a rating of 750.
This rating is assumed to be based on 0 games ().
- Step 2:
- Calculate the ``effective'' number of games played
by each player.
This number, which is typically less than the actual number
of games played, reflects the uncertainty in one's rating,
and is substantially smaller especially when the player's rating is low.
This value is used in the ``special'' and
``standard'' rating calculations.
See Section 2.1 for the details of the computation.
- Step 3:
- Calculate a first rating estimate for each unrated player.
For most unrated players, this involves
using the ``special'' rating formula (see Section 2.2).
Exceptions include unrated players with high FIDE ratings,
and unrated quick chess players with standard ratings based
on 9 or 10 games.
Let the ``prior'' rating, , and the number of games, ,
be the values assigned from Step 1.
However, for only this step in the computation, set the number of
effective games to 1 for each unrated player having a Step 1
rating based on games.
- If an opponent of the unrated player has a pre-event rating,
use this rating in the ``special'' rating formula.
- If an opponent of the unrated player is also unrated,
then use the initial rating imputed from Step 1.
If the resulting rating from Step 3 for the unrated player
is less than 100, then change the rating to 100.
- Step 4:
- For every player,
calculate an intermediate rating with
the appropriate rating formula.
- If a player is unrated, use the ``special'' rating formula
with initial ``prior'' rating, , from Step 1.
The effective number of games for unrated players is the
value determined from Step 2.
- If a player has played 8 or fewer games (),
or if a player's game outcomes in all previous events have been
either all wins or all losses,
then use the ``special'' rating
formula, with ``prior'' rating, , equal to the player's
pre-event rating.
- If a player has completed more than 8 games () and
has not had either all wins or all losses,
use the ``standard'' rating formula (see Section 2.3).
In the calculations, use the opponents' pre-event
ratings in the computation (for players with pre-event
ratings), or the results of the Step 3 ratings for unrated opponents.
If the resulting rating from Step 4 is less than 100,
then change the rating to 100.
- Step 5:
- Repeat the calculations from Step 4 for every
player, again using a player's pre-event rating (or the
results of Step 1 for unrated players)
to perform the calculation,
but using the results of Step 4 for the opponents' ratings.
If the resulting rating from Step 5 is less than 100,
then change the rating to 100.
These five steps result in the new set of post-event ratings
for all players.
Next: Details of the Rating
Up: The USCF Rating System
Previous: The USCF Rating System
Mark Glickman
2004-09-22