In the planning and design of new clinical trials, calculation of the required sample size and power is a critical part of the process. Power calculations are usually based on quantities estimated from analysis of historical data and are therefore subject to uncertainty. In many cases this is addressed by sensitivity analysis, but simple sensitivity analysis gives an incomplete picture of the u...

In this paper I address the question-how large is a phylogenetic sample? I propose a definition of a phylogenetic effective sample size for Brownian motion and Ornstein-Uhlenbeck processes-the regression effective sample size. I discuss how mutual information can be used to define an effective sample size in the non-normal process case and compare these two definitions to an already present con...

WHY Calculating the sample size is essential to reduce the cost of a study and to prove the hypothesis effectively. HOW Referring to pilot studies and previous research studies, we can choose a proper hypothesis and simplify the studies by using a website or Microsoft Excel sheet that contains formulas for calculating sample size in the beginning stage of the study. MORE There are numerous ...

Optimum sample size is an essential component of any research. The main purpose of the sample size calculation is to determine the number of samples needed to detect significant changes in clinical parameters, treatment effects or associations after data gathering. It is not uncommon for studies to be underpowered and thereby fail to detect the existing treatment effects due to inadequate sampl...

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Relative risk is usually the parameter of interest in epidemiologic and medical studies. In this paper, the author proposes a modified Poisson regression approach (i.e., Poisson regression with a robust error variance) to estimate this effect measure directly. A simple 2-by-2 table is used to justify the validity of this approach. Results from a limited simulation study indicate that this appro...

Noninferiority trials comparing new treatment with an active standard control are becoming increasingly common. This article discusses relevant issues regarding their need, design, analysis and interpretation: the appropriate choice of control group, types of noninferiority trial, ethical considerations, sample size determination and potential pitfalls to consider.

The term "design" encompasses all the structural aspects of a study, notably the definition of the study sample, size of sample, method of treatment allocation, type of statistical design (randomised, cross-over, sequential, etc), and choice of outcome measures. The importance of this stage cannot be overemphasised since no amount of clever analysis later will be able to compensate for major de...

Sample size estimation is a major component of the design of virtually every experiment in medicine. Prudent use of the available prior information is a crucial element of experimental planning. Most sample size formulae in current use employ this information only in the form of point estimates, even though it is usually more accurately expressed as a distribution over a range of values. In thi...