[1] It was an assessment of Thoroughbred racehorses issued by the International Federation of Horseracing Authorities (IFHA) in January 2010.
[2] It included horses aged three or older which competed in flat races during 2009.
This year's highest rating was awarded to Sea the Stars for his performance in the Irish Champion Stakes.
A total of 333 horses were included in the list, 45 more than the previous year.
It also shows the leading performers in various subdivisions of each group, which are defined by the distances of races, and the surfaces on which they are run.