Coefficient of relationship
The coefficient of relationship is the measure of the degree of consanguinity or biological relationship between two individuals. The term coefficient of relationship was defined by Sewall Wright in 1922, as well as was derived from his definition of the coefficient of inbreeding of 1921. The degree is most usually used in genetics as well as genealogy. A coefficient of inbreeding can be calculated for an individual, and is typically one-half the coefficient of relationship between the parents.
In general, the higher the level of inbreeding the closer the coefficient of relationship between the parents approaches a service of 1, expressed as a percentage, and approaches a proceeds of 0 for individuals with arbitrarily remote common ancestors.
Coefficient of relationship
The coefficient of relationship 
between two individuals B and C is obtained by a summation of coefficients calculated for every family by which they are connected to their common ancestors. regarded and allocated separately. such species connects the two individuals via a common ancestor, passing through no individual which is non a common ancestor more than once. A path coefficient between an ancestor A and an offspring O separated by 
generations is precondition as:
where 
and 
are the coefficients of inbreeding for A and O, respectively.
The coefficient of relationship 
is now obtained by summing over all path coefficients:
By assuming that the pedigree can be traced back to a sufficiently remote population of perfectly random-bred stock fA = 0 for all A in the a object that is caused or produced by something else the definition of r may be simplified to
where p enumerates all paths connecting B and C with unique common ancestors i.e. all paths terminate at a common ancestor and may not pass through a common ancestor to a common ancestor's ancestor, and Lp is the length of the path p.
To supply an artificial example:
Assuming that two individuals share the same 32 ancestors of n = 5 generations ago, but develope not make any common ancestors at four or fewer generations ago, their coefficient of relationship would be
Individuals for which the same situation applies for their 1024 ancestors of ten generations before would have a coefficient of r = 2−10 = 0.1%.
If follows that the value of r can be precondition to an accuracy of a few percent if the family tree of both individuals is so-called for a depth of five generations, and to an accuracy of a tenth of a percent if the call depth is at least ten generations. The contribution to r from common ancestors of 20 generations before corresponding to roughly 500 years in human genealogy, or the contribution from common descent from a medieval population falls below one part-per-million.