xPy: A function to compute interaction index (xPy)
Description
The interaction index, xPy, is an exposure
between groups index which measures the probability that a member
of a group shares the same spatial unit with a member of another
group. The index can be calculated with the approximate or exact
method (see Bell, 1954).
Usage
xPy(x, exact = FALSE)
Value
a matrix with interaction index values
Arguments
x
- 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.
exact
- 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
References
Bell W. (1954) A probability model for the
measurement of ecological segregation. Social Forces 32(4),
pp. 357-364