Any measure of the similarity of two samples. In ecological work, the similarity index devised in 1913 by J. Czekanowki has been widely used. This measures similarity as C = 2W/(a + b), where a and b are the quantities of all the plants (or another commodity) found in the 2 stands, or other units to be compared, and W is the sum of the lesser values for those species common to both units. Complete similarity thus scores 1, complete dissimilarity 0. See also affinity index.
Subjects: Plant Sciences and Forestry.