TOBA: Thoroughbred Owners and Breeders Association
Owner Education

Explanation of Performance and Production Indexes

When you read through the Stakes Winners section of The Blood-Horse and the Stakes Results section of Thoroughbred Times, you will notice the performance summaries of stallions contain production indexes such as SI, AEI, CI, ComSI, etc. Below, these indexes and other performance and production indexes found in the above-mentioned publications as well as other publications are defined.

Racing Index (RI)
The RI is based on the average earnings per start of runners in North America. The RI is calculated by taking all foals born in a given year and determining that crop's average earnings per start for each year that it raced. Colts and fillies are separated for the calculation. After five years of racing, a runner's RI does not change, even if it continues to race. The average earnings per start for a crop for a given year is set at 1.00. A RI of 2.00 would have earned twice as much per start during a given year as a horse of the same sex, from the same crop with a RI of 1.00

Sire Index (SI)
An average of the RIs for all of the stallion's foals that have started three or more times in North America.

Comparable Sire Index (ComSI)
The average of the RIs of progeny produced from mares bred to subject stallion, excluding foals by subject stallion.

Average Earnings Index (AEI)
An index of the lifetime earnings of a sire's runners compared to the average of all runners in the same years; average earnings of all runners in a given year is set at 1.00.

Comparable Index (CI)
The average earnings of progeny produced by mares bred to one stallion when they were bred to other stallions.

Broodmare Sire Index (BSI)
An average of the RI of all foals out of the sire's daughters that started at least three times. For BSI to be calculated, a broodmare sire must be represented by a minimum of 75 starters lifetime.

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