Journal Article

Sample size calculations: basic principles and common pitfalls

Marlies Noordzij, Giovanni Tripepi, Friedo W Dekker, Carmine Zoccali, Michael W Tanck and Kitty J Jager

in Nephrology Dialysis Transplantation

Published on behalf of European Renal Association - European Dialysis and Transplant Assoc

Volume 25, issue 5, pages 1388-1393
Published in print May 2010 | ISSN: 0931-0509
Published online January 2010 | e-ISSN: 1460-2385 | DOI:
Sample size calculations: basic principles and common pitfalls

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One of the most common requests that statisticians get from investigators are sample size calculations or sample size justifications. The sample size is the number of patients or other experimental units included in a study, and determining the sample size required to answer the research question is one of the first steps in designing a study.

Although most statistical textbooks describe techniques for sample size calculation, it is often difficult for investigators to decide which method to use. There are many formulas available which can be applied for different types of data and study designs. However, all of these formulas should be used with caution since they are sensitive to errors, and small differences in selected parameters can lead to large differences in the sample size. In this paper, we discuss the basic principles of sample size calculations, the most common pitfalls and the reporting of these calculations.

Keywords: epidemiology; nephrology; power; sample size; statistics

Journal Article.  4092 words.  Illustrated.

Subjects: Nephrology

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