How the COI is calculated
Every dog page and every test mating shows three figures: the COI, the AVK and the pedigree completeness. Here is what they mean and how the site works them out.
The coefficient of inbreeding (COI)
The COI is the probability that a dog inherited two identical copies of the same gene from one ancestor, one through its sire and one through its dam. The higher it is, the more closely related the parents are.
We use Wright's coefficient of inbreeding, the standard method used by kennel clubs and most pedigree software:
COI = Σ (½)n₁ + n₂ + 1 × (1 + FA)
- For every common ancestor A, found on both the sire's side and the dam's side, every path that links the sire and the dam through A is counted.
- n₁ and n₂ are the number of generations between the sire and A, and between the dam and A.
- FA is the ancestor's own inbreeding coefficient: an inbred common ancestor counts more.
In practice, the site computes this with the kinship (coancestry) method: the COI of a dog is the kinship between its sire and its dam, worked out step by step through the whole pedigree. It gives exactly the same result as adding up Wright's paths one by one, but it is faster and no path can be missed.
Some reference values
| Mating | COI of the litter |
|---|---|
| Parent × offspring, or full brother × sister | 25% |
| Half brother × half sister | 12.5% |
| First cousins | 6.25% |
| Second cousins | 1.56% |
These values assume the common ancestors are not inbred themselves. If they are, the COI is higher.
Why the number of generations matters
The COI is always calculated over a fixed number of generations: 5 by default, and you can choose from 3 to 10 just above the figures. A deeper or more complete pedigree finds more common ancestors, so it gives a higher COI. Two dogs can only be compared over the same number of generations.
The AVK (ancestor loss coefficient)
The AVK is the number of distinct ancestors divided by the number of possible ancestor slots. Over 5 generations there are 62 slots. 100% means no ancestor appears twice; the lower the AVK, the more often the same dogs come back in the pedigree.
Pedigree completeness
This is the share of ancestor slots actually filled in. Unknown ancestors cannot be counted, so a pedigree with many gaps shows a COI that is lower than reality, and an AVK that looks worse than it is. Always read the three figures together.
Common ancestors
Under the COI, the page lists the common ancestors found on both sides. In the pedigree tree, an ancestor that appears several times is shown in the same colour each time, so you can spot it at a glance.