The isolation index, xPx, is an exposure index that measures the probability that two members of a group share the same spatial unit. This index can be calculated using the approximate or the exact method (see Bell, 1954).
- an object of class matrix (or which can be coerced to that class), where each column represents the distribution of a group within spatial units. The number of columns should be greater than 1 (at least 2 groups are required). You should not include a column with total population, because this will be interpreted as a group.
- a logical variable to specifiy the index version: exact = FALSE (by default) for the approximate version of the index, and exact = TRUE for the exact version
a numeric vector containing the isolation index value for each group
Bell W. (1954) A probability model for the measurement of ecological segregation. Social Forces 32(4), pp. 357-364
1 2 3
 0.7500 0.9211  0.7475 0.9203
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