 For two sets of data with "m" and "n" observations, the set of two-element sets made of them is their Cartesian product, which contains "m" × "n" pairs of points (one from each set); each such pair defines one difference of values.The Hodges–Lehmann statistic is the median of the "m" × "n" differences.For a population that is symmetric, the Hodges–Lehmann statistic estimates the population's median.