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This infrequently-used diversity measure was proposed by Kempton and Taylor (1976). It measures the interquartile slope of the cumulative abundance curve and is estimated by :
where nr = the total number of species with abundance R;
S = the total number of species in the sample;
R1 and R2 the 25% and 75% quartiles of the cumulative species curve;
nR1 = the number of individuals in the class where R1 falls;
nR2 = the number of individuals in the class where R2 falls.
This index has been little used, probably because of the difficulties of computation. It seems worth considering; see Magurran (2000).
To compare two indices see Testing for significant differences between indices.
A simple plot of the way the index changes between samples is displayed by clicking on the Graph tab on the output window.