Power and sample size

Power and sample size estimations are measures of how many patients are needed in a study. Nearly all clinical studies entail studying a sample of patients with a particular characteristic rather than the whole population. We then use this sample to draw inferences about the whole population.

- Jones et al.: An introduction to power and sample size estimation

If you want to understand

• power and sample size estimation
• why power is an important part of both study design and analysis
• the differences between sample size calculations in comparative and diagnostic studies and

• learn how to perform a sample size calculation

read the article of S R Jones et al., An introduction to power and sample size estimation.

More introduction to power can be found from Online Statistics Education and its Power chapter.

A series of educational letters explaining methods to calculate the sample size for various clinical research study designs have been published in the Advanced Journal of Emergency Medicine:

• Sample Size Calculation Guide - Part 1: How to Calculate the Sample Size Based on the Prevalence Rate.
• Sample Size Calculation Guide - Part 2: How to Calculate the Sample Size for an Independent Cohort Study.
• Sample Size Calculation Guide - Part 3: How to Calculate the Sample Size for an Independent Case-control Study.
• Sample Size Calculation Guide - Part 4: How to Calculate the Sample Size for a Diagnostic Test Accuracy Study based on Sensitivity, Specificity, and the Area Under the ROC Curve.