<P> The coefficient of relationship is sometimes used to express degrees of kinship in numeric terms in human genealogy . </P> <P> In human relationships, the value of the coefficient of relationship is usually calculated based on the knowledge of a full family tree extending to a comparatively small number of generations, perhaps of the order of three or four . As explained above, the value for the coefficient of relationship so calculated is thus a lower bound, with an actual value that may be up to a few percent higher . The value is accurate to within 1% if the full family tree of both individuals is known to a depth of seven generations . </P> <Table> <Tr> <Th> Degree of relationship </Th> <Th> Relationship </Th> <Th> Coefficient of relationship (r) </Th> </Tr> <Tr> <Td> 0 </Td> <Td> identical twins; clones </Td> <Td> 100% (1) </Td> </Tr> <Tr> <Td> </Td> <Td> parent--offspring </Td> <Td> 50% (2) </Td> </Tr> <Tr> <Td> </Td> <Td> full siblings </Td> <Td> 50% (2 + 2) </Td> </Tr> <Tr> <Td> </Td> <Td> 3 / 4 siblings or sibling--cousins </Td> <Td> 37.5% (2 + 2) </Td> </Tr> <Tr> <Td> </Td> <Td> grandparent--grandchild </Td> <Td> 25% (2) </Td> </Tr> <Tr> <Td> </Td> <Td> half siblings </Td> <Td> 25% (2) </Td> </Tr> <Tr> <Td> </Td> <Td> aunt / uncle--nephew / niece </Td> <Td> 25% (2 ⋅ 2) </Td> </Tr> <Tr> <Td> </Td> <Td> double first cousins </Td> <Td> 25% (4 ⋅ 2) </Td> </Tr> <Tr> <Td> </Td> <Td> great grandparent--great grandchild </Td> <Td> 12.5% (2) </Td> </Tr> <Tr> <Td> </Td> <Td> first cousins </Td> <Td> 12.5% (2 ⋅ 2) </Td> </Tr> <Tr> <Td> 6 </Td> <Td> quadruple second cousins </Td> <Td> 12.5% (8 ⋅ 2) </Td> </Tr> <Tr> <Td> 6 </Td> <Td> triple second cousins </Td> <Td> 9.38% (6 ⋅ 2) </Td> </Tr> <Tr> <Td> </Td> <Td> half - first cousins </Td> <Td> 6.25% (2) </Td> </Tr> <Tr> <Td> 5 </Td> <Td> first cousins once removed </Td> <Td> 6.25% (2 ⋅ 2) </Td> </Tr> <Tr> <Td> 6 </Td> <Td> double second cousins </Td> <Td> 6.25% (4 ⋅ 2) </Td> </Tr> <Tr> <Td> 6 </Td> <Td> second cousins </Td> <Td> 3.13% (2 ⋅ 2) </Td> </Tr> <Tr> <Td> 8 </Td> <Td> third cousins </Td> <Td> 0.78% (2 ⋅ 2) </Td> </Tr> <Tr> <Td> 10 </Td> <Td> fourth cousins </Td> <Td> 0.20% (2 ⋅ 2) </Td> </Tr> </Table> <Tr> <Th> Degree of relationship </Th> <Th> Relationship </Th> <Th> Coefficient of relationship (r) </Th> </Tr>

What is the measure of relatedness (r) between first cousins
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