Studies of the effects of patch size and isolation on plant species density have yielded contrasting results. However, much of the available evidence comes from relatively recent anthropogenic forest fragments which have not reached equilibrium between extinction and immigration. This is a critical issue because the theory clearly states that only when equilibrium has been reached can the numbe...

Interactions measured on the additive scale are more relevant than multiplicative interaction for assessing public health importance and also more closely related to notions of mechanistic synergism. Most work on sample size and power calculations for interaction have focused on the multiplicative scale. Here we derive analytic expressions for sample size and power calculations for interactions...

The effects of sample size on fitting length distribution of wood particles used for manufacturing wood-based composites were investigated. A simulation study was conducted to evaluate the variations of the first four sample moments and the ability of the sample distributions to characterize the population represented by the original data. Results showed that a sample size of 2000 was deemed ne...

We describe and compare four different methods for estimating sample size and power, when the primary outcome of the study is a Health Related Quality of Life (HRQoL) measure. These methods are: 1. assuming a Normal distribution and comparing two means; 2. using a non-parametric method; 3. Whitehead's method based on the proportional odds model; 4. the bootstrap. We illustrate the various metho...

Sequential tests outperform fixed sample size tests by requiring fewer samples on average to achieve the same level of error performance. The Sequential Probability Ratio Test (SPRT) has been suggested by Wald [1] for sequential binary hypothesis testing problems. SPRT recursively calculates the likelihood of an observed data stream and requires this likelihood to be stored in memory between sa...

In this paper, a Bayesian approach is developed for simultaneously comparing multiple experimental treatments with a common control treatment in an exploratory clinical trial. The sample size is set to ensure that, at the end of the study, there will be at least one treatment for which the investigators have a strong belief that it is better than control, or else they have a strong belief that ...

The fact that characters may co-vary in organism groups because of shared ancestry and not always because of functional correlations was the initial rationale for developing phylogenetic comparative methods. Here we point out a case where similarity due to shared ancestry can produce an undesired effect when conducting an independent contrasts analysis. Under special circumstances, using a low ...

Addressing a sample size is a practical issue that has to be solved during planning and designing stage of the study. The aim of any clinical research is to detect the actual difference between two groups (power) and to provide an estimate of the difference with a reasonable accuracy (precision). Hence, researchers should do a priori estimate of sample size well ahead, before conducting the stu...

BACKGROUND Epidemiological studies of exposures that vary with time require an additional level of methodological complexity to account for the time-dependence of exposure. This study compares a nested case-control approach for the study of time-dependent exposure with cohort analysis using Cox regression including time-dependent covariates. METHODS A cohort of 1340 subjects with four fixed a...

The Editor has invited me to mark the occasion with a few words "on the development and/or impact of randomised trials over the last decade, or perhaps some thoughts about the future." I do so here by citing some recent developments that give me cause for both pride about the present state of randomised controlled trials (RCTs) and optimism about their future. Respecting the sample size of Jame...