Yorkshire Chess
Association |
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update: |
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Grade
Calculation |
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Grades
are calculated annually, using games played from 1st May to the following 30th April as
their basis.
When a
batch of results is being graded, it is necessary first to ascribe working grades to each
ungraded player. This working grade may be
calculated from as many of the player's games as are available. Where leagues, for example, are graded at the end
of the season, all games played by an ungraded player are used to calculate this working
grade. The better computer grading programs
calculate working grades for all ungraded players in the system at the end of the grading
period by recursive methods (feeding the results back into the calculation over and over
again), as this best copes with games where one ungraded player has played a number other
ungraded players.
For each
of a player's games from the relevant period, a score is calculated on the basis of the
opponent's grade (or working grade for ungraded opponents) and the result of the game. If an opponent's grade (or working grade) is more
than forty more/less than the player's grade, then for this calculation the effective
grade of that opponent is taken as exactly forty more/less.
A player's score for a win is the opponent's grade (or working grade) plus fifty;
for a draw it is exactly the opponent's grade (or working grade), and for a loss it is the
opponent's grade (or working grade) less fifty. The
player's scores from the games are totalled, and the games are counted.
If the
number of a player's graded games from the latest season (the season being graded) is 30
or more, then only those games are used in calculating the player's grade.
Less
than 30 games are regarded as too few to for a statistically viable sample, so attempts
are made to supplement those results with games 'borrowed' from the previous one or two
seasons. This results in a grade which is
more an average grade over a period of more than one season than a measurement of the
player's performance in a single season. This
is held more reliable than a grade based on too few games.
The games 'borrowed' are not actual games, but average results for the season in
question. The number of points scored for
each 'borrowed game' from a previous season is the total number of points scored that
season divided by the number of games involved.
If the
number of games from the latest season is less than 30, but enough games can be borrowed
from the previous season to top then up to 30, then that is done. If the number of games from the latest season and
the previous season together total less than thirty, but enough games can be borrowed from
the season before that to top the total up to 30, then that is done. If the games from the latest three seasons total
less than 30, then all the games from those three seasons are used.
The
player's new grade is the number of points scored from the games included, divided by the
number of games. Grades in the list have
prefixed to them a letter (A to E) to categorise them in terms of the number of games used
in the calculation, the seasons from which the games were derived, and the number of those
games derived from the latest season, as detailed on Grade
Categories. Interpretation of the grade
should be in the light of this category. For
an example of the calculation of a grade see Grading Calculation Examples