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Yorkshire
Chess Association |
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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