Dosage: Pedigree & Performance
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What Is Aptitudinal Type?

The fundamental hypothesis of contemporary Dosage theory is that a relationship exists between aptitudinal type and performance on the track.  Said differently, the hypothesis proposes that the inherited characteristics of a horse as expressed by its pedigree should correlate with the horse’s competitive profile. 

When we talk about a horse’s “inherited characteristics”, what do we mean?  We’ll begin by dividing a runner’s traits into three broad categories.  These are not meant to be exclusive, and within each there is a wide distribution of attributes.  For our purposes, however, we will limit ourselves to this simplified model because on the one hand it does address the issue while on the other it avoids the impossibility of dealing with the infinite potential variations.

The first category is distance preference.  Is the horse more successful running short or does it do better running long?  Second is surface preference.  Does the horse have a greater affinity for dirt racing or for turf racing?  Third is maturation rate.  Is the horse precocious or is it late developing?

The following illustration shows the eight possible combinations of these traits.  The symbols used in the drawing include, in the distance category, S for sprint and R for route.  In the surface category, D is for dirt and T is for turf.  The maturation rate category is divided into E for early maturing and L for late developing.

With this technique we can visualize how the variations relate to one another and distinguish, for example, an early-developing dirt sprinter (SDE) from a late-developing turf router (RTL).

Early-maturing dirt sprinters (SDE)
Late-maturing dirt sprinters (SDL)
Early-maturing turf sprinters (STE)
Late-maturing turf sprinters (STL)
Early-maturing dirt routers (RDE)
Late-maturing dirt routers (RDL)
Early-maturing turf routers (RTE)
Late-maturing turf routers (RTL)

Next we employ a Dosage metric in order to determine if there really is a difference between the Dosage characteristics of a horse and its aptiitudinal type as defined in the illustration.  The metric we use is the Center of Distribution (CD) which, because it is a linear scale, is the most statistically useful and most accurate Dosage figure.

Our approach is to determine the average CD for each variation (i.e., aptitudinal type) to see how the specific combinations of traits are reflected in the Dosage figures. 

We calculate the average CD using data from the table in the article at this site entitled “The Relationship Between the DI and the CD: DP Patterns”, updated for 2015 and based on 29,394 North American open stakes races since 1983.  We then rank order the categories of distance, surface and maturity corresponding to the columns %SPR, %TURF and %2YO in the table.  The highest percentage in each category is considered most representative of that trait and the average CD associated with it is noted.  A high %SPR means a higher percentage of wins at shorter distances.  A high %TURF means a higher percentage of wins on grass.  A high %2YO means a higher percentage of juvenile wins.  Conversely, the lowest percentage in each category is considered most unrepresentative of that trait and the average CD associated with it is noted as well.  In the SDE case, for example, we use the average CD for the categories with the highest %SPR, lowest %TURF and highest %2YO.  Knowing how many examples there are associated with the average CD in each category we are able to calculate an overall average CD for the SDE aptitudinal type.  The details are shown below.

Highest %SPR: sample size = 735, average CD = 1.08
Lowest %TURF: sample size = 588, average CD = 1.11
Highest %2YO: sample size = 206, average CD = 1.68

The overall average CD for the SDE aptitudinal type is 1.17 (735*1.08+588*1.11+206*1.68)/(735+588+206).

The following table displays the overall average CD for each of the eight aptitudinal types.

Aptitudinal Type Average CD
SDE 1.17
SDL 0.58
STE 0.93
STL 0.24
RDE 0.76
RDL 0.37
RTE 0.50
RTL 0.08

Immediately we note how Dosage figures are able to capture distinctions in aptitudinal type.  The difference between early-maturing dirt sprinters (SDE, average CD 1.17) and late-maturing turf routers (RTL average CD 0.08) is especially dramatic.  Even within overlapping aptitudinal types we can see significant separation.  For example, in all cases where the only difference is between sprint and route, the sprint type has the higher CD (SDE>RDE; SDL>RDL; STE>RTE; STL>RTL).  When the only difference is between dirt and turf we observe SDE>STE, SDL>STL, RDE>RTE and RDL>RTL where the dirt type always has the higher CD.  Finally, when the only difference is between early maturing and late developing we find SDE>SDL, STE>STL, RDE>RDL and RTE>RTL and the early-maturing type always has the higher CD.  From this we conclude that shorter distances, dirt and early maturity are associated with speed in a pedigree as captured by the Dosage figures.  Similarly, we conclude that longer distances, turf and late maturity are associated with stamina in a pedigree.  Each of the other combinations, or aptitudinal types, expresses a unique balance of inherited speed and stamina.

These results confirm that Dosage methodology does indeed capture the relationship between a Thoroughbred’s aptitudinal type and how that type is expressed in the real world of racing.