The signed rank statistic S is computed as

where is the rank of after discarding values of , and n is the number of values not equal to . Average ranks are used for tied values.
If , the significance of S is computed from the exact distribution of S, where the distribution is a convolution of scaled binomial distributions. When , the significance of S is computed by treating

as a Student t variate with degrees of freedom. V is computed as

where the sum is over groups tied in absolute value and where is the number of values in the ith group (Iman 1974, Conover 1980). The null hypothesis tested is that the mean (or median) is , assuming that the distribution is symmetric. Refer to Lehmann (1998).