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In recent years, McWilliams and Tajuddin have proposed new and more powerful non-parametric tests of symmetry for continuous distributions about a known center. In this paper, we propose a simple non-parametric two-stage procedure based on the sign test and a percentile-modified two-sample Wilcoxon test. The small-sample properties of this test, Tajuddin's test, McWilliams' test and a modified runs test of Modarres and Gastwirth are investigated in a Monte Carlo simulation study. The simulations indicate that, for a wide variety of asymmetric alternatives in the lambda family, the hybrid test is more powerful than are existing tests in the literature.

We define the lens depth (LD) function LD(t; F ) of a vector t ∈ R d with respect to a distribution function F to be the probability that t is contained in a random hyper-lens formed by the intersection of two closed balls centred at two i.i.d observations from F . We show that LD is a statistical depth function and explore its properties, including affine invariance, symmetry, maximality at the centre and monotonicity. We define the sample LD and investigate its uniform consistency, asymptotic normality and computational complexity in high-dimensional settings. We define the lens median (LM), a multivariate analogue of the univariate median, as the point where the LD is maximised. The sample LM is the vector that is covered by the most number of hyper-lenses formed between any two sample observations. We state its asymptotic consistency and normality and examine its breakdown point and relative efficiency. The sample LM is robust and efficient for estimating the centre of a unimodal distribution. A comparison of LD and LM to existing data depth functions and medians in terms of computational complexity, robustness, efficiency and breakdown point is presented.

We will show that the regression approach to estimating the standard error of the Gini index can produce incorrect results as it does not account for the correlations introduced in the error terms once the data are ordered. To assess the effect of ignoring the correlation in the error terms we examined two distributions and show that the regression method overestimates the standard error of the Gini index. We recommend that the more mathematically complex or computationally intensive methods be used.

Building a minimal spanning tree. Library of Congress Cataloging-in-Publication Data Good, Phillip I. Permutation tests: a practical guide to resampling inethods for testing hypothesesjPhillip Good. p. cm.-(Springer series in statistics) Inc1udes bibliographical references and index. 1. Statistical hypothesis testing. 2. Resampling (Statistics) I. Title. 11. Series.