Understanding the Exact Score and Similar Score (CSI)
Learn how the Exact Score (E) and Similar Score (CSI) measure pedigree similarity in G1 Goldmine and Stallion Match. This guide explains what each score means, why they can differ, and how to interpret them when analysing thoroughbred pedigrees.
When Stallion Match finds a Similar Stakes Winner, it displays two percentage scores: Exact Score (E) and Similar Score (CSI). Each score compares the stakes winner's pedigree with the hypothetical mating you searched, but they measure a different type of similarity.
The key difference
Exact Score measures matches in the same pedigree position. Similar Score measures shared ancestry across both the sire and dam sides, even when the matching ancestors appear in different positions.
What is the Exact Score (E)?
The Exact Score shows how closely the structure of the two pedigrees matches within five generations.
It calculates the percentage of ancestors that appear in both pedigrees in the same pedigree position. For example, an ancestor only counts as an Exact match when it appears in the corresponding position in each pedigree.
How to read it
A higher Exact Score means more ancestors appear in the same positions, so the overall structure of the two pedigrees is more closely matched.
Simple example
Pedigree A: Danehill appears as the sire's damsire.
Pedigree B: Danehill also appears as the sire's damsire.
Result: This is an Exact match because Danehill appears in the same position in both pedigrees.
If Danehill appeared elsewhere on the sire side in Pedigree B, it would not count as an Exact positional match, although it may still contribute to the Similar Score.
What is the Similar Score (CSI)?
The Similar Score shows how much common ancestry the two pedigrees share across both the sire side and the dam side within five generations.
Unlike the Exact Score, the matching ancestors do not need to appear in the same pedigree position. An ancestor can contribute when it appears anywhere on the corresponding side of both pedigrees: sire side with sire side, or dam side with dam side.
The sire-side and dam-side match counts are combined and converted into a percentage using the maximum possible score of 31 horses on one side of a five-generation pedigree.
How to read it
A higher Similar Score means the two pedigrees share more common ancestry across both their sire and dam sides.
Simple example
Pedigree A: Danehill appears on the sire side.
Pedigree B: Danehill also appears on the sire side, but in a different position.
Result: This can contribute to the Similar Score because the ancestor appears on the same side of both pedigrees, even though the exact position is different.
Exact Score and Similar Score compared
|
Score |
What it measures |
What counts as a match |
|---|---|---|
|
Exact Score (E) |
How closely the pedigree structures match. | The same ancestor appears in the same pedigree position within five generations. |
|
Similar Score (CSI) |
How much common ancestry is shared across both sides. | The same ancestor appears on the corresponding sire or dam side, regardless of its position within that side. |
Why can the Similar Score be lower than the Exact Score?
It may seem logical that the broader Similar Score should always be higher than the Exact Score. However, the scores use different calculation methods and measure different aspects of pedigree similarity, so they should not be compared as though one is a broader version of the other.
The Exact Score rewards matching ancestors in identical pedigree positions. The Similar Score combines the strength of the matches found across both sides of the pedigree. As a result, a pedigree can have several strong positional matches but a lower Similar Score when the shared ancestry is unevenly distributed between the sire and dam sides.
Important
A lower Similar Score does not mean the result is incorrect. It simply reflects a different type of pedigree similarity from the Exact Score.
Why can the Similar Score be 0%?
The Similar Score considers the shared ancestry found across both the sire and dam sides. It may display 0% when matching ancestors are found on only one side of the pedigrees.
For example, the two pedigrees may share several ancestors on the sire side but have no qualifying matches on the dam side. Because the Similar Score combines the two sides, the resulting score may be zero.
This does not necessarily mean the pedigrees have no ancestors in common. It means the matches do not meet the Similar Score's requirement for shared ancestry across both sides.
Which score should I focus on?
Neither score is better or more important in every situation. They are designed to be considered together:
- Exact Score helps you understand how closely the two pedigrees match in structure.
- Similar Score helps you understand how much common ancestry is shared across both the sire and dam sides.
Viewed together, the two scores provide a more complete picture of how the Similar Stakes Winner’s pedigree compares with your hypothetical mating.
Remember
These scores measure pedigree similarity only. A high Exact Score or Similar Score does not guarantee racing success and should be considered alongside the full Similar Stakes Winners results and other available analysis.
Frequently asked questions
Does a higher percentage always mean a better mating?
Not necessarily. A higher percentage means the pedigrees are more similar according to that score. It is not a standalone rating of mating quality and does not guarantee a successful outcome.
Can the Similar Score be higher than the Exact Score?
Yes. This can occur when the pedigrees share many ancestors on the corresponding sire and dam sides, but those ancestors appear in different positions.
Why are the Exact Score and Similar Score calculated differently?
They are designed to identify different patterns. Exact Score measures matching pedigree structure, while Similar Score measures shared ancestry across both sides of the pedigree.
Do ancestors outside five generations affect these scores?
No. Both scores are calculated using the sire and dam lines within the first five generations.
Does the Similar Score compare a sire-side ancestor with the dam side?
No. Sire-side ancestors are compared with the sire side, and dam-side ancestors are compared with the dam side.
What does CSI mean?
CSI is the label used for the Similar Score in Stallion Match. It measures shared ancestry across both the sire and dam sides within five generations.
Quick summary
| Score Type | Meaning |
|---|---|
| Exact Score (E) | Percentage of ancestors appearing in the same pedigree positions within five generations. |
| Similar Score (CSI) | Percentage representing shared ancestry across both the sire and dam sides within five generations, regardless of position within each side. |