Editing Dosage Index (section)

==Method==
The index itself is compiled by noting the presence of certain influential sires, known as ''[[chefs-de-race]]'' ([[French language|French]] for "chiefs of racing", or, more esoterically, "masters of the breed") in the first four generations of a horse's pedigree.  Based on what distances the progeny of the sires so designated excelled in during their racing careers (the distance preferences displayed by the sires themselves while racing being irrelevant), each chef-de-race (the list released in the early 1980s identified 120 such sires, {{as of|2019|10|lc=on}} there are 232 horses on the list<ref>{{Cite web |date=20 October 2019 |title=Chefs-de-Race as of October 2019 (listed alphabetically) |url=http://i.bloodhorse.com/pdfs/ChefdeRace%20Alpha%20List_updated%20Oct2019.pdf |access-date=29 January 2023 |website=Bloodhorse |format=PDF}}</ref>) is placed in one or two of the following categories, or "aptitudinal groups": Brilliant, Intermediate, Classic, Solid or Professional, with "Brilliant" indicating that the sire's progeny fared best at very short distances and "Professional" denoting a propensity for very long races on the part of the sire's offspring, the other three categories ranking along the same continuum in the aforementioned order.  If a chef-de-race is placed in two different aptitudinal groups, in no case can the two groups be more than two positions apart; for example, Classic-Solid or Brilliant-Classic are permissible, but Brilliant-Solid, Intermediate-Professional and Brilliant-Professional are not.

If a horse's sire is on the chef-de-race list, it counts 16 points for the group to which the sire belongs (or eight in each of two categories if the sire was placed in two groups); a grandsire counts eight points, a great-grandsire four, and a great-great-grandsire two (female progenitors do not count directly, but if any of their sires etc. are on the chef-de-race list points would accrue via such sires).

This results in a Dosage Profile consisting of five separate figures, listed in order of Brilliant-Intermediate-Classic-Solid-Professional.  [[Secretariat (racehorse)|Secretariat]], the 1973 [[Triple Crown of Thoroughbred Racing|Triple Crown]] winner, for example, had a Dosage Profile of 20-14-7-9-0.  To arrive at the Dosage Index, the first two figures plus one-half the value of the third figure are added together, and then divided by one-half of the third figure plus the sum of the last two figures.  In this case, it would be 37.5 (20 + 14+ 3.5) divided by 12.5 (3.5 + 9 + 0), giving Secretariat a Dosage Index of exactly 3.00 (the figure almost always being expressed with two places to the right of the decimal point and rounded to the nearest 0.01).

A second mathematical value, called the Center of Distribution, can also be computed from the Dosage Profile.  To determine this value, the number of Brilliant points in the profile is doubled, and added to the number of Intermediate points; from this is then subtracted the number of Solid points and twice the number of Professional points.  The result is then divided by the total number of points in the entire profile, including the Classic points.  In Secretariat's case, this would work out as 54 (40 + 14) minus 9 (9 + 0) divided by 50 (20 + 14 + 7 + 9 + 0), yielding a Center of Distribution of 0.90 (the figure nearly always being rounded to the nearest 100th of a point, as with the Dosage Index).

High Dosage Index (and Center of Distribution) figures are associated with a tendency to perform best over shorter distances, while low numbers signify an inherent preference for longer races.  The median Dosage Index of contemporary North American [[thoroughbred]]s is estimated at 2.40 (the ''average'' figure being impossible to calculate because some horses have a Dosage Index of "infinity," a scenario which arises when a horse has only Brilliant and/or Intermediate chef-de-race influences in its Dosage Profile).  The average Center of Distribution for modern-day North American race horses is believed to be approximately 0.70 (both Dosage Index and Center of Distribution figures tend to be lower for European thoroughbreds because in Europe the races are longer on aggregate and European breeders thus place greater emphasis on breeding their horses for stamina rather than speed).