39In statistics, the 4th order cumulant of a random variable x is equal to κ4 = ⟨(x − ⟨x⟩)4⟩− 3⟨(x − ⟨x⟩)2⟩ and κ2 = ⟨(x − ⟨x ⟩)2⟩ , so that U = − κ4∕3κ2 for x = m and ⟨m ⟩ = 0 .