Correlation as Probability of Common Descent

We highlight one interpretation of Pearson's r (largely unknown to behavioral scientists), inspired by the genetic measurement of inbreeding. The coefficient of inbreeding, defined as the probability that two paired alleles originate from common descent, equals the correlation between the uniting gametes. We specify the statistical conditions under which r can be interpreted as probability of identity by descent and explore the possibility of generalizing that meaning of correlation beyond the inbreeding context. Extensions to the framework of agreement between judges and to that of sequential dependencies are considered. Viewing correlation as probability is heuristically promising. We examine the implications of this approach in the case of three types of bivariate distributions and discuss potential insights and risks.