A correction for including competitive asymmetry in measures of local interference in plant populations.

In 1989, Thomas and Weiner described a method to measure the degree of competitive symmetry in plant populations in which the performance of a focal plant is explained as a function of the size and number of its neighbors. However, if plant size is correlated with plant performance, then Thomas and Weiner's method may give misleading results. Statistically controlling for the effect of plant size on performance corrects the problem and highlights the observation that size is an important determinant of plant growth rate.