Asymptotic tail approximations for some nonparametric test statistics

We give some asymptotic approximations for the upper tail probabilities of two nonparametric test statistics, namely the Wilcoxon signed-rank statistic and Kendall's tau coefficient. Then, we provide numerical comparisons, by comparing the exact probabilities with a normal approximation, a classical saddlepoint approximation, a Lugannani and Rice saddlepoint approximation and an Edgeworth expansion.