The ATR Durability Index
In an effort to help our clients and readers better assess a sire's ability to get sound and durable offspring, we've devised the ATR Durability Index, an objective system for evaluating the longevity of a stallion's foals as a function of multiple variables.
In recent years, The Jockey Club and various trade publications have published sire lists based on average number of starts per foal/starter, and while these are certainly the cornerstones of evaluating soundness, they are merely a starting point for a full analysis. These lists fail to take into account the racing class of a sire's progeny and how they may be impacting a sire's statistical profile.
For our system, we incorporated what we felt were the four most important descriptive statistics when studying soundness: 1) percentage of starters from live foals, 2) average number of starts per starter, 3) average earnings per start, and 4) relationships between AEI/CI and SI/ComSI systems (click here for a detailed explanation). These four variables were weighted accordingly and standardized on a 0 to 100 scale with the following parameters:
| Variable |
Percentage |
Scale (representing 0 to 100 percent) |
| % starters from foals |
34.6% |
65 to 95 |
| Avg. starts per starter |
26.9% |
9 to 26 |
| Avg. earnings per start |
26.9% |
2,000 to 12,000 |
| AEI/CI, SI/ComSI analysis |
11.5% |
-40 to 20 |
It's not enough to simply pull together the correct statistics. For a system to be useful, the different variables must be weighted so that the end result is a distinguishing index that gives users an accurate view of a sire's influence. Additionally, each variable has to be scaled properly to prevent skewing. For our ratings, we converted the raw numbers for each variable onto a zero to 100 scale before weighing them relative to each other.
Perhaps the most important distinction made by our system is the one made by a sire's average earnings per start. Obviously, one cannot compare two stallions who appear equal in most ways when one has an average earnings per start of $6,500, and the other $2,800. The latter is much more likely to stay sound simply because they're not competing against such grueling competition. An allowance or deduction is needed on each end of this statistical spectrum.
To insure against small and misleading sample sizes, a durability index is given only to sires with at least 75 live foals who were at least four years old when the most recent Thoroughbred Times Stallion Directory was published. The percentage of starters from foals only utilizes crops four years old and older so as to not incorporate two and three year olds who could still make it to the races. Average starts per starter and average earnings per start are computed after excluding the sire's current crop of two year olds.
Because we lack the manpower of a large organization, this will be a work in progress. We'll make every effort to add 1-3 stallions per day during the week. If there are stallions that you'd like to have included, please contact us by clicking here. (Last updated: 12/16/08)
| SIRE |
DURABILITY INDEX |
GRADE |
** indicates most recent addition(s) to rankings
