Morisita's overlap index

Morisita's overlap index

Morisita's overlap index, named after Masaaki Morisita, is a statistical measure of dispersion of individuals in a population. It is used to compare overlap among samples (Morisita 1959). This formula is based on the assumption that increasing the size of the samples will increase the diversity because it will include different habitats (i.e. different faunas).

Formula:

C_D= \frac{2\sum_{i=1}^S x_i y_i }{(D_x + D_y) XY }
xi is the number of times species i is represented in the total X from one sample.
yi is the number of times species i is represented in the total Y from another sample.
Dx and Dy are the Simpson's index values for the x and y samples respectively.
— Completely different samples
If the species occur in the same proportions in both samples, then CD = 1.

Horn's modification of the index is (Horn 1966)**:

C_H= \frac{ 2 \sum_{i=1}^S x_i y_i }{ \left( {\sum_{i=1}^S x_i^2 \over X^2} + {\sum_{i=1}^S y_i^2 \over Y^2} \right) X Y } \,.

External links

References

  • Morisita, M. (1959). "Measuring of the dispersion and analysis of distribution patterns". Memoires of the Faculty of Science, Kyushu University, Series E. Biology. 2: 215–235.
  • Morisita, M. (1962). "Iδ-Index, A Measure of Dispersion of Individuals". Researches on Population Ecology, volume 4, number 1, pages 1–7.
    • Horn, H. S. (1966). Measurement of "Overlap" in comparative ecological studies. The American Naturalist 100:419-424.


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