Dosage: Pedigree & Performance
The Top 100 Sires and Broodmare Sires through 2009 by Proficiency Index (PI)
The Proficiency Index, or PI, is a proprietary measure of sire performance based on a combination of stakes production and progeny earnings. We derive the PI in such a way that sires deficient in either category are penalized relative to sires that excel in both. Therefore, a sire with progeny earnings concentrated in just a few outstanding runners or a sire with a high percentage of stakes winners in low valued races will earn a low PI figure compared to a sire with a high percentage of stakes winners in high valued races. The national average PI for all sires is 1.00.
The PI is calculated using the sire's Average-Earnings Index (AEI) and his Stakes-Winner Index (SWI). The AEI, as described in The Blood-Horse magazine, "indicates how much purse money the progeny of one sire has earned, on the average, in relation to the average earnings of all runners in the same years." If the purse money earned is twice the average, the AEI is 2.00.
Similarly, the SWI indicates the lifetime percentage of stakes winners by one sire in relation to the average percentage of stakes winners for all sires. If the percentage of stakes winners is twice the average, the SWI is also 2.00.
The equation for calculating the PI is 2x(AEIxSWI)/(AEI+SWI). By illustration, if a sire has an AEI of 2.00 and a SWI of 2.00, the calculation is:
PI = 2x(2.00x2.00)/(2.00+2.00) = 8.00/4.00 = 2.00
An example of a sire having most of his earnings in relatively few stakes winners is a sire with an AEI of 3.00 but an SWI of only 1.00.
PI = 2x(3.00x1.00)/(3.00+1.00) = 6.00/4.00 = 1.50
In the first example both earnings AND stakes production are well above average. In the second the PI is lower because although earnings are high, stakes production is only average.
Similarly, a sire with many stakes winners in low-valued races (e.g., regional sires with a high percentage of state-bred stakes winners) might have an AEI of only 1.00 with a SWI of 3.00. His PI would be the same as in the second example and lower than in the first.
PI = 2x(1.00x3.00)/(1.00+3.00) = 6.00/4.00 = 1.50
An advantage of PI over other methods of measuring sire performance is the ability to differentiate between stallions who continuously sire top class runners in many important races from those who earn a reputation from only a few prominent performers or those who are consistent producers but of lower class stakes winners.
Sires include those that stand or stood (deceased) in North America (stallions exported prior to the 2006 breeding season are excluded), and have runners in North America.
Broodmare sires are included regardless of the stallion's origin or the country in which he stands or stood.
