Identification of the Bray-Curtis similarity index: Comment on Yoshioka (2008)

In a recent As I See It, Yoshioka (2008, Mar Ecol Prog Ser 368:309-310) stated that the term Bray-Curtis should only be used for doubly-standardised data, and when data counts are used to calculate similarity, the term Czekanowski is correct; by using the wrong name, it is claimed, marine ecologists demonstrate a lack of knowledge and introduce confusion. This needs to be recti- fied. It is incorrect: (1) to confuse pretreatment of data with calculation of similarity (although both are part of a process, few ecologists would accept that it is logical for the name of a coefficient to alter depending on the data used to calculate it); (2) that the name for the coefficient calculated from counts is Czekanowski; (3) that terrestrial ecologists reserve the name Bray-Curtis for doubly- standardised data; (4) to assume that alternative names for coefficients cause confusion when it is clear which coefficient is used; (5) that this is a problem with software, or the way software is used. Yoshioka (2008) is right that pretreatments alter the rank order of similarities between samples, but this is not a novel observation, and it is why ecologists who know what they are doing use different pre-treatments. What ecologists mean by Bray-Curtis is well understood, and they do not mean Czekanowski's coefficient as originally described, although some textbooks confuse the 2 indices. We should maintain use of the term Bray-Curtis in community ecology.

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