World Gastroenterology Organisation

Global Guardian of Digestive Health. Serving the World.

Education & Training

Sample Size Calculation

The purpose of this portion of the WGO research module will be to assist researchers with sample size calculations for their research projects. In addition, links will be provided to internet sites where free statistical tools are available for researchers. Proposed content will include the following:

It is very important during the planning phase of a clinical trial to determine how many participants you will need to answer your clinical question. Too many participants can be a waste of resources and time, and too few participants will not produce a reliable answer.

Choosing a sample size is a combination of considerations. These include (1) the number of participants you can reasonably expect to recruit in the given time period with the resources you have available, and (2) a mathematical calculation. The final figure will be the minimum number of participants you require to reliably answer your research question.

There are many software packages dedicated to performing sample size/power calculations, in addition to a number of free links of the Internet. Below you will find a number of links to assist you with your sample size calculation:

Calculating Sample Size:

Links to additional resources:

  1. "Determining the sample size in a clinical trial" by Adrienne Kirby, Val Gebski and Anthony C Keech. Med J Aust 2002; 177: 256-57
  2. Statistical considerations for clinical trials and scientific experiments
  3. Java Applets for power and sample size.
  4. A wide variety of more complicated trial design is available at


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