Coefficient of inbreeding (COI) is a measure of the probability that an allele inherited from each parent will be ‘identical by descent’, ie, derived from the same ancestor. It is a measure of inbreeding as the same ancestor must appear on both sides of the pedigree for there to be a measurable COI. It is dependant upon the number of generations being used within the calculation, and this should be stated when giving the COI.
A higher value indicates a more inbred individual, and the value is expressed as a percentage. For the most accurate analysis, as many generations as possible should be used. Be wary of missing data within a pedigree as this could give a false impression of a low score.
The reason COI is of interest is because of the possibility of inheriting the same deleterious recessive mutation from a single ancestor through both the sire and the dam. And therefore having or breeding an individual which may express in their phenotype any simple recessive mutation in their genotype.
It is generally considered good practice when planning future matings to ensure the COI is less than the breed average (according to our data currently 6.5% in ten generations) but to balance that decision with other factors such as, health results and temperament of the proposed parents.
IWDB is using a simple path-counting mechanism to calculate COI.
Coefficient of Inbreeding is available in the Ancestors Pane of iwdb.org