We consider the situation in two sample testing when one variance is assumed to be known while the other variance is considered unknown. This situation arises, for example, when one is interested in comparing a standard treatment with a new treatment. Although this situation occurs relatively infrequently, our example discusses the important tool of moment matching and makes the classic two sam...

BACKGROUND During the last 30 years, the median sample size of research studies published in high-impact medical journals has increased manyfold, while the use of non-parametric tests has increased at the expense of t-tests. This paper explores this paradoxical practice and illustrates its consequences. METHODS A simulation study is used to compare the rejection rates of the Wilcoxon-Mann-Whi...

The behaviour of group sequential tests in the two-sample problem is investigated if one replaces the classical non-robust estimators in the t-test statistic by modern robust estimators of location and scale. Hampel's 3-part redescending M-estimator 25A used in the Princeton study and the robust scale estimators length of the shortest half proposed by Rousseeuw & Leroy and Q proposed by Roussee...

Ask experts what would be an important reduction in amount consumed. Need some idea of the SD of a within-child difference in consumption from a four hour period in one day to a four hour period in another day. Could do a pilot study with say 10 children measured [without any intervention] on two different days and get the SD of the 10 differences. Then use sample size formula for 1 sample t-te...