Dosage: Pedigree & Performance
Dosage Inflation in the Kentucky Derby
Although some critics might point to the 2009 Kentucky Derby victory of Mine That Bird, a horse currently with a DI of 5.40 and a CD of 1.19, as evidence of the irrelevance of Dosage theory, they would be wrong. And they would be wrong because their understanding of Dosage almost surely comes from an uninformed turf media and not from the actual source. This isn't something new. Misinformation about Dosage and the Kentucky Derby has been flowing freely for almost 30 years, ever since our original observation in the early 1980s that no winner of the Derby since at least 1940 had a DI over 4.00 was improperly interpreted as no horse with a DI over 4.00 "could" win the Derby. The latter conclusion is clearly nonsense and not any different from saying no African-American could be elected president of the United States. But just as the social evolution of America has opened the presidential door to people of color, evolutionary trends within the Thoroughbred race horse have altered the type of horses winning classic races. Even the critics acknowledge the ever-increasing influence of speed in the Thoroughbred, yet they seem completely unaware that Dosage, simply a pedigree classification system and methodology for monitoring aptitudinal evolution within the breed over time, has been tracking these changes from the very beginning.
Although Dosage, in fact any theory based on empirical observation, is rightfully subject to constructive criticism in order to improve it, many critics make their case based on a false interpretation of the original DI 4.00 guideline while also being unaware that Dosage actually confirms what they know intuitively, that speed in Thoroughbred pedigrees is continually increasing.
We have been writing about the increase in speed in the Thoroughbred since the publication of our original paper on Dosage in Daily Racing Form in 1981. In fact, we have published information even defining the rate at which that speed is increasing. Data confirming the trend in three-year-old colts was revealed in the Daily Racing Form articles where it was shown that the average DI of champions was 1.43 between 1941 and 1950 and 2.46 between 1971 and 1980. This phenomenon is nothing new and the trend has been continuous for at least 60 years.
The charts below display the linear trend lines of the DI of Derby winners by year since 1940. The first chart covers the years 1940 to 1990, which is the year before the first horse with a DI greater 4.00, Strike the Gold, won. The second chart covers the years 1940 to 2010. In both cases the trend line is extended ahead in time to the year 2030.
It is immediately obvious that the trend lines are essentially identical with virtually the same slope and intercept values. Both charts suggest that half of all Derby winners by 2030 will have a DI above 4.00 unless there is a shift in breeding patterns toward more stamina. In other words, the trend remains unchanged over the last 20 years and Mine That Bird is an integral part of it. It is always unexpected when a horse wins at over 50 to 1 odds, but recent history tells us that it is not unexpected when a horse wins with a DI over 4.00. That is the direction of Thoroughbred breeding and the sooner the public places the original DI 4.00 guideline in perspective the better.
A separate issue is how one defines classic performance. Is it simply by virtue of winning a classic race or is it by comparison with classic standards? Certainly no one would equate recent Derby performances of Mine That Bird, Giacomo, Charismatic, Real Quiet or Strike The Gold (all with a race-time DI over 4.00) with those of Secretariat, Affirmed, Seattle Slew or Spectacular Bid. One could reasonably ask whether there is a relationship between pedigree and the absolute quality of a classic performance. This issue is addressed elsewhere.
Finally, the specific case of Mine That Bird highlights something fundamental about Dosage methodology and that is the timeframe in which new chefs-de-race are identified. Dosage is unlike speed figures where the output is almost instantaneous and immediately applicable. Dosage takes time because the data required to statistically confirm prepotence for type is accumulated over years, not days or weeks or months. As a result, we have always cautioned users of Dosage figures to consider them a starting point and make modifications based on what they know about possible speed or stamina influences in the horse's pedigree. Many speed handicappers do essentially the same thing with published figures by taking into account the manner in which the figure was achieved, for example, loose on the lead or with a very wide trip. This modification approach is especially critical in a "young" pedigree where the sire or broodmare sire hasn't been producing long enough to establish any meaningful patterns. One can speculate, but one doesn't know until they do it. If it were easy, no one would have anticipated that classically-bred and classic distance winner Slewpy would be a premier sire of sprinters or that a speed-oriented sprinter/miler like Kingmambo would be a world-class sire of classic distance stayers. Accordingly, there may be as yet unidentified sources of prepotent stamina in Mine That Bird's pedigree, perhaps Birdstone or Smart Strike or even some other unrecognized influence. Most important, Dosage consistently has been publicized as a technique applied to large populations of Thoroughbreds. When applied to individuals there is always the possibility an individual may lie on the statistical distribution some distance from the center. Even so, it remains part of the population defined by the distribution.
In conclusion, the results of the 2009 Kentucky Derby had no bearing on the utility of Dosage as a technique for identifying prepotent aptitudinal type, as a way of correlating pedigree type with track performance in large populations or as a tool for monitoring the evolution of aptitudinal type within the breed. Those who expect more will be disappointed. Considering Mine That Bird's best three-year-old Beyer speed figure was 9 points lower than the best of any other Derby starter that raced in the US in 2009, I suppose speed handicappers were equally disappointed, although unlikely to toss the approach as a result.