 The method is now recognized as an algorithm that implements a special case of what are termed phylogenetic generalized least-squares models.The logic of the method is to use phylogenetic information (and an assumed Brownian motion like model of trait evolution) to transform the original tip data (mean values for a set of species) into values that are statistically independent and identically distributed.The algorithm involves computing values at internal nodes as an intermediate step, but they are generally not used for inferences by themselves.