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APEX (Annual Progeny Earnings indeX) ratings are a series of indexes, which rate stallions in 17 different categories of progeny performance. The signature index, which is called the 'A Runner Index', began life as an attempt to modify the impact of one huge earner (Spend A Buck, at the time, for his sire, Buckaroo, in 1985) on a sire's cumulative average earnings index. It does this by measuring the frequency with which a sire's runners reach the top two percent of earners, each year. In North America, this is now about $150,000, so any horse who earns that amount is designated an 'A Runner'. The next two percent (about $110,000, at the moment) are called 'B Runners,' and the next four percent (about $75,000) are 'C Runners.' Those three groups combined--the top eight percent--are called 'ABC Runners.
If the top two percent of all earners are designated as 'A Runners,' then a sire's A Runner Index is calculated by whether he has +/- two percent 'A Runners' from Runners in a year, and by how much. For A and B Runners, two percent equals an Index of 1.00, which is average. The higher the better: six percent A Runners equals a 3.00 A Runner Index. For C Runners, four percent equals 1.00, and when you combine A+B+C Runners, eight percent equals 1.00.
This method also enables us to combine or compare ratings in different regions, namely: North America (U.S. plus Canada); 'Europe' (Great Britain & Ireland, which are combined; France; and Germany); and Japan. Different thresholds for each category are established in each jurisdiction, and are then totaled up to give the overall picture. Of the 17 ratings (indices) for each sire, 12 are these regional and overall class gradations: A, B, and C Indexes in North America, Europe, Japan, and Overall. Then there is the Overall ABC Index, and four 'ABC Age Indices,' which tell us a stallion's proficiency at siring ABC Runners as two-year-olds; three- year-olds; four-year-olds; and five-year-olds and up. While the Overall A Runner Index is the most important rating, these other ratings often shed a very interesting light on what particular sires are really best at.
Finally, two other limitations: the indices are all calculated on what is called a 'rolling' seven-year timescale, meaning only the last seven years are used for these calculations (that puts once-great sires in a more current perspective); and only sires who had ten or more three-year-old foals of the last year covered are eligible for rating. That eliminates the bottom, and results in a scale where 1.00 really does equal average, whereas the cumulative average-earnings index tends to make sires look better than they really are, at least in the commercial sire world.
How APEX is Calculated - Apex indices are calculated in five different racing jurisdictions, then added together, and organized in three regions.
These are:
  • North America: US/Canada
  • Europe: Great Britain/Ireland (collected together), France, Germany
  • Japan
In each place, the top two percent of earners from all runners are identified each year, and these are called 'A Runners;' the next two percent are 'B Runners,' the next four percent 'C Runners,' and therefore the top eight percent are combined as 'ABC Runners.' Second, the calculations and analyses are restricted to the last seven years. We do that because we don't want to let once-great stallions live entirely on past glories--they have to have done something at least somewhat recently. Third, because of a practical quirk in the parameters (only rating sires who had at least 10 three-year-olds of the last season included), we kick out the bottom fifth of runners by hopeless stallions, and it results in a 1.00 rating really equating to an average stallion.
With the average-earnings index, which the APEX (Annual Progeny Earnings indeX) figures resemble in many ways, there is a natural inflation caused by including all runners by all stallions, so that 1.00 stallions on average-earnings index tables are actually below average.