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On E. C. Pielou's Index of Non-Randomness

M. D. Mountford
Journal of Ecology
Vol. 49, No. 2 (Jun., 1961), pp. 271-275
DOI: 10.2307/2257261
Stable URL: http://www.jstor.org/stable/2257261
Page Count: 5
Pielou has suggested that the quantity $\alpha = \pi D \bar\omega$, where D is the estimate of the density of a plant population derived from quadrat sampling and $\bar\omega$ is the mean of the squares of the distances from random points to the nearest plant, may be used as an index of non-randomness. In her treatment of the sampling properties of α, Pielou considers only the sampling variability of $\bar\omega$ and ignores the variability of D. The variance of α, corrected to allow for the sampling errors of both D and $\bar\omega$, is now given, and the test of nonrandomness and the test comparing two non-random indices are accordingly modified.