A statistic, introduced by Moran in 1950, that measures spatial autocorrelation using information only from specified pairs of spatial observations. Suppose there are n locations, the observed value at location j is x_j, and the overall mean value is x̄. Let w_jk=1 if the comparison of the value at location j to the value at location k is of interest, and let w_jk=0 otherwise. By definition, w_jj=0, for all j. Usually, the only comparisons of interest are those between immediate neighbours. The statistic is given by