<Bill.Venables <at> csiro.au> writes: > > That is interesting. The first of these, namely > > sum(|x_i - y_i|) / sum(x_i + y_i) > > is now better known in ecology as the Bray-Curtis distance. Even more interesting is the typo in Henry & > Stevens "A Primer of Ecology in R" where the Bray Curtis distance formula is actually the Canberra > distance (Eq. 10.2 p. 289). There seems to be a certain slipperiness of definition in this field.
Thank you for bringing to my attention the similarity of the Canberra and Bray-Curtis quantitative indices. Bray-Curtis dissimilarity can also, of course, be defined as 1 - 2w/(a+b) where w is sum of the minimum of each relevant pair of values, and a and b are the totals for sites a and b, respectively. These definitions appear to yield similar results, and to better reflect the original work by Bray and Curtis, I should probably define their distance as they did! Cheers, Martin Henry Hoffman Stevens (a.k.a. Hank) > > What surprises me most is why ecologists still cling to this way of doing things, It is one of the few places I > know of where the analysis is justified purely heuristically and not from any kind of explicit model for > the ecological processes under study. > > Bill Venables. > > > ______________________________________________ > R-devel <at> r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
