This review basically provided a conceptual framework for sample size calculation in epidemiologic studies with various designs and outcomes. The formula requirement of sample size was drawn based on statistical principles for both descriptive and comparative studies. The required sample size was estimated and presented graphically with different effect sizes and power of statistical test at 95...

We read with interest the paper of Estévez, et al, recently published in Hepatitis Monthly (1). That article was a Letter to the Editor on the study conducted by Nikui Nejad et al (2). One of the comments made by Estévez et al was on the adequacy of the size of the studied sample. They believed that the sample size was not adequate based on the provided data and the type of study (1). In the re...

A sample size with sufficient statistical power is critical to the success of genetic association studies to detect causal genes of human complex diseases. Genome-wide association studies require much larger sample sizes to achieve an adequate statistical power. We estimated the statistical power with increasing numbers of markers analyzed and compared the sample sizes that were required in cas...

Sample size must be determined while planning a study to ensure that valid conclusions can be drawn when the study is over. different formulae for calculating the required size of the sample are used for different study designs and situations. A computer program is described here to ease the complexity of calculation of sample size for studies designed to use students 't' test.

BACKGROUND Stepped wedge trials (SWTs) can be considered as a variant of a clustered randomised trial, although in many ways they embed additional complications from the point of view of statistical design and analysis. While the literature is rich for standard parallel or clustered randomised clinical trials (CRTs), it is much less so for SWTs. The specific features of SWTs need to be addresse...

This paper discusses the statistical principles, methods, and software programs used to calculate sample size. In addition, it reviews the practical challenges faced in calculating sample size. We show that because of such challenges, statistical calculations often do not provide us with a clear-cut number for the study sample size; rather they suggest a range of reasonable numbers. The paper a...

S size is a crucial component of research design. More often researchers want sample size to be justified on non statistical grounds. For example, a researcher may say that I could get only these many cases in the specified time period so as a statistician do something to make the study valid in spite of whatever sample size I have used. Similarly, financial constraint is sometimes cited an exc...