T-tests, non-parametric tests, and large studies--a paradox of statistical practice?

ABSTRACT:

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-Whitney (WMW) test and the two-sample t-test for increasing sample size. Samples are drawn from skewed distributions with equal means and medians but with a small difference in spread. A hypothetical case study is used for illustration and motivation.

Results

The WMW test produces, on average, smaller p-values than the t-test. This discrepancy increases with increasing sample size, s

SUBMITTER: Fagerland MW 

PROVIDER: S-EPMC3445820 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature