Following the ABSP membership's vote in favour of Steve Perry's proposal to increase the games in the ratings calculation from 100 to 150 on 1/1/2011, the following occurred.

On January 1 2011, I reset the ratings algorithm to the new parameters. For those who had played at least 100 ABSP-rated games in total, the first calculation of 2011 included 100 games (or slightly more because it contained only complete tournaments). The weight of the most recent game was 225.

From January 1 2011 onwards, new games have been added to the calculation until a player exceeds the new maximum of 150, at which point the oldest games are dropped as usual. Many of those who played at the 48-round UK Open reached 150 games on January 9th.

For the 1,671 players active in the previous 5 years, 92% had no ratings change on conversion, or a change of 1 point (up or down). No-one's rating changed by more than 4 points. The main reason for the bigger changes was where a player's oldest current tournament, which may have contributed only 1 or 2 games to the previous ratings calculation, was fully restored in the calculation. If that tournament performance differed significantly from the player's Dec 31st 2010 rating, there could be a 2 to 4 point change in the new rating.

Putting this one-off change into perspective, players who were active before 1999 may remember that for many players, a change of rating occurred every New Years Day, when a bundle of old games was discarded. I have no details of the range of changes, but I think changes of 5 or even 10 points on each New Years Day were not uncommon.

John Grayson
ABSP Ratings Officer