The statistics defined such that
where is a central moment. These statistics generalize h-statistics and were originally called "generalized -statistics" (Tracy and Gupta 1974). The term "polyache" was introduced by Rose and Smith (2002, p. 255) by way of analogy with the polykay statistic. Polyaches are commonly defined in terms of power sums, for example
Polyaches can be computed using PolyH[r, s, ...] in the Mathematica application package mathStatica.