IB Geography
The Index of Dissimilarity is used to compare the distribution of two variables, especially in different social or ethnic groups. The data MUST be in % form and the total of each column MUST be 100%. The index of dissimilarity ID is given by the formula above where x and y are values of each sample.
Example: comparison between the repartition of African-Americans and Whites in the United States:
Region of the US
% of African Americans
compared to total
African-American population
% of whites
compared to total
white population
|x-y|
South East
53%
28%
25%
North East
19%
25%
6%
Midwest
20%
29%
9%
West
8%
18%
10%
Sum
100%
100%
50%

Index of Dissimilarity ID = 0.5 x 50% = 25%

This means that 25% of the African American population in the US would have to change the region in which they live in in order to have the same relative distribution as the white population, or vice-versa. The distribution of both populations is therefore fairly dissimilar.