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The Ordination of Incidence Data
M. H. Williamson
Journal of Ecology
Vol. 66, No. 3 (Nov., 1978), pp. 911-920
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2259303
Page Count: 10
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(1) Principal components analysis of incidence (presence and absence) data produces a horseshoe effect. A new method, called step-across, is described which removes this effect. (2) From a matrix of joint occurrences, distances are found directly for all positive values. Distances for zero joint occurrences are found from the shortest network distance. The complete distance matrix is then analysed by Gower's principal coordinates technique. (3) The method can be used on both the rows and columns of an incidence matrix. It is illustrated with artificial data and with data on euphausiids from the Indian Ocean.
Journal of Ecology © 1978 British Ecological Society