Testing linear combinations of normal group means with unequal variances and possibly unequal samples sizes using a t-statistic is a well known problem for which the effective degrees of freedom are unknown. ? and ? set forth their approximations based on the ratio of combinations of fourth moments, and their methodology remains the de facto standard. We propose a new approach that extends thei...

Virzi (1992), Nielsen and Landauer (1993), and Lewis (1994) have published influential articles on the topic of sample size in usability testing. In these articles, the authors presented a mathematical model of problem discovery rates in usability testing. Using the problem discovery rate model, they showed that it was possible to determine the sample size needed to uncover a given proportion o...

We propose a framework for analyzing and comparing distributions, which we use to construct statistical tests to determine if two samples are drawn from different distributions. Our test statistic is the largest difference in expectations over functions in the unit ball of a reproducing kernel Hilbert space (RKHS), and is called the maximum mean discrepancy (MMD). We present two distributionfre...

The Wilcoxon one-sample signed rank test may be used to test whether a particular sample came from a population with a specified median. It is assumed that the population distribution is symmetric. The data consists of a single sample of n observations denoted by x1; x2; . . . ; xn. This sample may arise from the difference between pairs of observations from two matched samples of equal size ta...

By imposing directional decisions on traditional two-tailed tests, you will overestimate power, underestimate sample size, and ignore the risk of Type III error. You can avoid these problems by using the directional two-tailed test. This paper demonstrates how to use PROC POWER to estimate the prospective power and Type III error for one-sample, two-sample and paired t tests for means, and bino...

The goal of the two-sample test (a.k.a. the homogeneity test) is, given two sets of samples, to judge whether the probability distributions behind the samples are the same or not. In this paper, we propose a novel non-parametric method of two-sample test based on a least-squares density ratio estimator. Through various experiments, we show that the proposed method overall produces smaller type-...

BACKGROUND CONTEXT The nerve root sedimentation sign in transverse magnetic resonance imaging has been shown to discriminate well between selected patients with and without lumbar spinal stenosis (LSS), but the performance of this new test, when used in a broader patient population, is not yet known. PURPOSE To evaluate the clinical performance of the nerve root sedimentation sign in detectin...

Studies of genetic variation in natural populations at the sequence level usually show that most polymorphic sites are very asymmetrical in allele frequencies, with the rarer allele at a site near fixation. When the rarer allele at a site is present only a few times in the sample, say below five representatives, it becomes very difficult to detect linkage disequilibrium between sites from tests...