Dear R-helpers, There's a method named as in this message's subject that has been proposed by: Chen Y, Jackson DA, Harvey HH (1992) A comparison of von Bertalanffy and polynomial functions in modelling fish growth data. Canadian Journal of Fisheries and Aquatic Sciences 49:1228-1235. which is used to compare a group of non linear models. The method tests whether all the fitted curves describe the same population of data. The test is an F ratio: F = (RSSp - sum(RSSi) / DFp - sum(DFi)) / (sum(RSSi) / sum(DFi)) where the RSS and DF are the residual sum of squares and degrees of freedom, respectively. The 'p' and 'i' subscripts denote the pooled or each individual curve, respectively. If this procedure has already been implemented in a package, I'd be happy to hear about it. A search of the archives and other sources didn't help. Cheers, -- Sebastian Luque