dissimilarity index

A measurement of the overall difference between two percentage distributions. It is calculated by adding together the differences between the numbers in each pair of corresponding values and halving the total. The result shows the proportion of cases that would need to be reallocated in order to make the two distributions the same. Dissimilarity indices are often used in studies of occupational, or racial, segregation, or to summarize the difference between pairs of marginal distributions; for example, to compare class of origin and destination for internal migration, or to investigate differences between nations, sexes, and so on. Whether or not a dissimilarity will appear on a map will often depend oh the size of the units used. See modifiable areal unit.