[Rd] Canberra distance
hstevens at muohio.edu
Mon Feb 8 19:30:05 CET 2010
<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!
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.
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