STUDY OBJECTIVE To explore how Student's t test, which assumes normal errors, is affected by the nonnormal distribution of Glasgow Coma Scale (GCS) scores. METHODS A sample of 145,295 GCS scores from the Pennsylvania Trauma Systems Foundation was assumed to represent the true GCS distribution. Four Monte Carlo simulations, each based on 40,000 replications, were conducted to approximate the d...

For the assessment of agreement using probability criteria, we obtain an exact test, and for sample sizes exceeding 30, we give a bootstrap-t test that is remarkably accurate. We show that for assessing agreement, the total deviation index approach of Lin (2000, Statist. Med., 19, 255–270) is not consistent and may not preserve its asymptotic nominal level, and that the coverage probability app...

Faecal glucocorticoid metabolite (FGM) concentrations are used increasingly as a non-invasive measure to index physiological stress experienced by diverse taxa. However, FGM may not be evenly distributed throughout a faecal mass or faecal pellet group. Moreover, within-sample variation in FGM measurements associated with different sampling and/or processing techniques is rarely reported despite...

Injury Prevention recently published a commentary critical of epidemiological approaches to cycling safety. The author, Kary, suggests that our paper, which reanalysed Walker’s study of motor vehicle overtaking distance for cyclists, made false claims about type I errors and confused statistical significance and clinical significance. Kary supports this critique, along with other points in the ...

Positive Darwinian selection at the molecular level is often studied by comparing the number of synonymous nucleotide substitutions per synonymous site (d,) and the number of nonsynonymous substitutions per nonsynonymous site (dN) between homologous gene sequences, and a t-test with an infinite number of degrees of freedom is usually used for determining the statistical significance of the diff...

OBJECTIVE To determine the relationship between anthropometric indices and the age of menarche in female students of Sabzevar, Iran. METHODS The cross-sectional study was conducted in Sabzevar, Iran, from April to September 2010, and involved girls of 11-18 years of age. The required sample size for analysing the relationship between menarche age and Body Mass Index was estimated to be 110 by...

In the design of a randomized clinical trial with one pre and multiple post randomized assessments of the outcome variable, one needs to account for the repeated measures in determining the appropriate sample size. Unfortunately, one seldom has a good estimate of the variance of the outcome measure, let alone the correlations among the measurements over time. We show how sample sizes can be cal...

Due to the small number of replicates in typical gene microarray experiments, the performance of statistical inference is often unsatisfactory without some form of information-sharing across genes. In this article, we propose an enhanced quantile rank score test (EQRS) for detecting differential expression in GeneChip studies by analyzing the quantiles of gene intensity distributions through pr...

Effective management of wetland quantity and quality is crucial for effective conservation of declining amphibian populations. In particular, frogs and toads that employ aggregative breeding strategies may suffer negative population impacts in response to changes in availability of aquatic breeding habitat, including overabundance of suitable habitat, if density of conspecifics attending aggreg...

BACKGROUND Bleeding time test is used to assess the function of platelets in human body. The aim of this project was thus to estimate the sample size required to determine the normal range of bleeding time (BT) in Borujerd (a city in Iran). A pilot study was designed to determine the range of normal BT in a small group of normal people. The total sample size for the next study was then calculat...