Allometric extension

Constants of allometric growth are commonly estimated by the first eigenvec tor of the covariance matrix of log measurements. Hills (1982, in Encyclope dia of Statistical Sciences, 48-54) defines a model of allometric extension for two related species by the conditions that (a) the constants of allome tric growth are identical for both species and (b) the vector of mean diffe rences is proportional to the common first eigenvector of both covariance m atrices. We give a test for allometric extension and discuss estimation of the parameters of the allometric extension model, including standard errors .