Sample size and power calculations made simple

Abstract

Background Sample size estimation is an important concern for researchers as guidelines must be adhered to for ethics committees, grant applications and publications. Studies may be underpowered (too few participants) or overpowered (too many participants) so it is important to achieve the correct balance. Content The process of sample size calculations, including relevant definitions, is explained and clear examples for different study designs are provided for illustration. A range of software packages and websites are discussed and evaluated. Conclusions The information regarding sample sizes and statistical programs should be useful for researchers in order to perform sample size calculations for research projects.