Does Pedigree Matter Any Longer in the Kentucky Derby?

The startling upset wins by Giacomo in the 2005 Kentucky Derby and Mine That Bird in the 2009 Kentucky Derby, both at odds of greater than 50-1 and both with a DI over 4.00, have led to speculation that pedigree may no longer be as important as it once was in defining the classic American Thoroughbred. After all, Giacomo's sire, Holy Bull, had previously sired only one major stakes winner on the dirt at a distance beyond nine furlongs. That horse was Thunder Blitz, winner of Aqueduct's 2003 Grade 3 Queens County Handicap at 9½ furlongs and beaten in Monarchos' 2001 Kentucky Derby by almost nine lengths. Adding to concern about Holy Bull as a classic sire was the short 7.65 furlong average winning distance of his progeny in North American open stakes races. Mine That Bird's sire, Birdstone, although a classic winner, is a young sire with no established pattern regarding the distance capability of his get. One can speculate about the type he should transmit; however, there are numerous examples of sprinting sires consistently getting stayers and vice versa. You can't know how they will produce until they do.

The situation is complicated by the recent Derby wins of Smarty Jones in 2004, Funny Cide in 2003 and War Emblem in 2002. They were all sired by young stallions, none of which had ever won a stakes race beyond a mile. Elusive Quality, sire of Smarty Jones, and Distorted Humor, sire of Funny Cide, were noted for their blazing speed, the former setting a world record for a mile on the turf and the latter setting the seven-furlong track record at Churchill Downs. War Emblem's sire, Our Emblem, could do no better than place in graded stakes races at seven and eight furlongs. There is little to indicate from their racing careers that they would become classic sires early in their stud career. Of course, the sire side of a pedigree is just one half of the equation. A speed sire alone doesn't preclude the possibility of a classically-bred, aptitudinally-balanced pedigree. Which brings us to Dosage.

Following a half century of Derby wins by horses with a Dosage Index (DI) of 4.00 or less, we have seen five winners exceeding that figure since 1991, including Giacomo and Mine That Bird. Now for many people these events are proof that Dosage has lost its usefulness or never was useful in the first place. That may be an obvious conclusion for those who considered Dosage to be only a mysterious magic formula for handicapping the Kentucky Derby. More than likely they are unaware that Dosage is, in fact, a pedigree classification system intended to monitor the dynamic changes in the relationship between pedigree type and track performance. If pedigree type is truly evolving, Dosage will capture the nature of that evolutionary process very well.

Dosage methodology has enabled us to observe an "inflation" factor in the DI of Derby winners for many years. Plotting the DI of Derby winners by year since 1940 and subjecting the data to linear regression yields a trend line indicating an average increase of more than 0.03 DI units per year over the last 70 years. This trend is depicted graphically in Chart 1.

Extending the trend line 15 years into the future strongly suggests that in the absence of a dramatic shift in breeding patterns we can expect half of all Derby winners by 2025 to have a DI over the previous historical guideline figure of 4.00. This alone is compelling evidence that the pedigree type of Derby winners is constantly evolving toward greater speed, a development that is troubling to traditionalists who believe excessive speed in pedigrees is a detriment to the Thoroughbred and undermines the meaning of classicity.

Similarly, we can observe a parallel rise in the overall speed of entire Kentucky Derby fields over the same timeframe as seen in Chart 2

Separately, we can look at the DI of Kentucky Derby starters relative to their finishing position in the race. This is shown in Charts 3 and 4 where we see a pattern in which lower DI starters have a history of finishing closer to the front than do higher DI starters. Chart 3 displays the trend line of the average DI by each finish position while Chart 4 shows the trend line when the DI of all the individual Derby starters are included, not just the average by finish position. It's clear that more stoutly bred horses have a competitive advantage at the classic distance.

But even if we accept that the pedigree type of Derby winners is changing, we are still confronted by the question of whether the changes we see have made pedigree less important to Derby performance. One way of addressing the question is to attempt a correlation of the quality of individual Kentucky Derbies with the pedigree type of the winners. How can we do this?

One measure of race quality is through the use of speed figures that tell us how fast a race was actually run. Speed figures are preferable to the raw final time of a race because time can be dramatically affected by track speed on a given day. Perhaps the longest established, widely known and most reliable speed figures available to the general public are those published by Andrew Beyer, long-time racing columnist for the Washington Post. Beyer, an internationally respected turf writer and handicapper, has been publishing his figures for quite some time, providing us with a good historical record.

The complementary historical pedigree type of Derby winners is available using Dosage figures.

The following table displays the DI of all Derby winners since 1991 along with the Beyer Speed Figure (BSF) for each year's Derby. We use 1991 as the starting point because that year was the first in which the historical DI 4.00 guideline was exceeded and it represents a dramatic shift in the pedigree type of Derby winners. The DI used in the table is the DI of the winner at the time of his Derby win and does not reflect any subsequent changes resulting from the addition of new chefs-de-race. The reader will notice that five of the lowest nine BSFs assigned by Andrew Beyer, an outspoken critic of Dosage, belong to the five winners with a DI above 4.00. The nine highest BSFs belong to Derby winners with a DI of 4.00 or less. Beyer's Kentucky Derby average par figure is 108.9, which none of the five DI>4.00 horses achieved. Without him knowing it, Beyer's own data confirm a correlation between Dosage and Kentucky Derby performance.

YEAR	DERBY WINNER	DI	BSF
1991	Strike the Gold	9.00	107
1992	Lil E. Tee	3.00	107
1993	Sea Hero	1.12	105
1994	Go For Gin	1.00	112
1995	Thunder Gulch	4.00	108
1996	Grindstone	1.44	112
1997	Silver Charm	1.22	115
1998	Real Quiet	5.29	107
1999	Charismatic	5.22	108
2000	Fusaichi Pegasus	3.67	108
2001	Monarchos	1.40	116
2002	War Emblem	3.40	114
2003	Funny Cide	1.53	109
2004	Smarty Jones	3.40	107
2005	Giacomo	4.33	100
2006	Barbaro	1.81	111
2007	Street Sense	2.14	110
2008	Big Brown	1.67	109
2009	Mine That Bird	5.40	105
2010	Super Saver	3.00	104
2011	Animal Kingdom	1.67	103

Chart 5 plots the DI against the BSF. The red line is the trend line derived by linear regression.

Although we see the expected typical scatter in the data, the trend line is quite revealing. The slant of the line from upper left to lower right indicates that the higher BSFs are associated with lower DIs. Said another way, Derby winners with more stamina-oriented pedigrees tend to run faster and earn better speed figures. Of course there are exceptions, such as War Emblem with DI 3.40, BSF 114 and Sea Hero with DI 1.12, BSF 105. However, the purpose of a statistical analysis is not to show that every member of a population with a common characteristic fits the population profile, Rather, the purpose is to demonstrate whether separate populations, each sharing unique characteristics, are the same or different. In this case we are trying to determine if Derby winners with higher DIs (i.e., relatively more inherited speed in their pedigree) have exhibited a different level of performance in the Derby than winners with lower DIs (i.e., relatively more inherited stamina). Note in this study that there are two clusters in the data, one group (or population) with DI 3.00 and above and another group (or population) with DI below 3.00. A statistical t-test showing whether the two populations are different from one another by more than mere chance yields the following result when we compare the BSFs of the two groups.

Perhaps most important to this analysis is the P-value of 0.03, suggesting that even though the sample sizes are relatively small, the difference observed between the two groups is statistically significant. It tells us that there is only about a 3% likelihood that the difference we see in the average BSFs for the two groups is the result of chance. For reference, a P-value of 0.05 or less indicates statistical significance.

We can extend the analysis to include the other American classics, the Preakness and the Belmont, to see if the observations made for the Kentucky Derby apply more broadly. The chart and statistical t-test provides similar results.

From this brief analysis we may interpret the result to mean that pedigree actually does still make a difference in the Kentucky Derby as well as the Preakness and Belmont, not necessarily in terms of which horse will win, but rather in terms of the quality of the classic performance. We have seen several classic winners with DIs over 4.00 in the last few years, but they belong to a group of speedier-bred horses that have not performed as well as their stouter-bred counterparts. Apparently not all classic races are created equal, and at least in recent years that inequality correlates especially well with the pedigree type of the winners. Stamina, required to stay a classic distance in classic horse time, is still a great asset. When a horse not traditionally bred to stay a classic distance wins a classic race, there is a reasonable probability that the race will fall short of historical classic standards.

	DI<3 (Avg=1.50)	DI>=3 (Avg=4.52)
BSF Average	110.2	106.8
P-value	0.03

	DI<=2 (Avg=1.51)	DI>=4 (Avg=5.08)	DI>2 & <4 (Avg=2.83)
BSF Average	109.6	105.7	108.5
P-value	0.03