ABSTRACT
Sample size and power calculations should always be performed in the planning stages of a study.
It is important to have a sample of the right size to allow a clinically relevant effect to be detected. The power of a study is related to sample size calculation.
This Chapter explains sample size and power and discusses the factors that are involved in their calculation.
Altman’s nomogram and an internet-based sample size calculator are both explained and used to calculate sample size. Step-by-step instructions are provided for their use in two example situations using both the nomogram and the web-based calculator.
