Power and Sample Size

Description: Accessibly-written webpage about the fundamentals of power and sample size.


Who is this resource for: Clinical investigators

Who created this resource: This site is run by the University of California Los Angeles Institute for Digital Research and Education.

What does this resource offer: This webpage is an excellent read for an investigator looking for a thorough description of the basics of power and how they pertain to planning a research study. Overall the language is informal and accessible to those with little statistical training. Major topics include knowing your research project, what you need to know to do a power analysis, obtaining the necessary numbers to do a power analysis, and factors that affect power. There is also a discussion about the issues of small sample sizes and sampling variation, multiplicity, and post-hoc power analyses. Examples are given using SPSS Sample Power, but they are still useful for understanding power and sample size calculations in other software.

Helpful hints: If you’re short on time, check out the “Conclusions” section at the end of the page.