Sample Size Considerations: Basics for Preparing Clinical or Basic Research.

Background: Sample size estimation is an important and integral part of a research protocol. While "how large a sample?" is a simple question, the answer is only meaningful within the context of the research question. Methods: Clear definitions of the variable of interest and target population parameters are key to estimating sample size. In turn the sample must be sized such that it can accurately detect the 'effect' of interest, adequately represent the target population and maintain maximum design efficiency. Four basic pieces of information are utilized in most sample estimation across all clinical research: significance level, power, magnitude of effect and variability of the variable of interest. Results/Discussion: Preliminary determination of these will greatly facilitate work with a biostatistician or a computer application to create a sample size estimation. While applications can support relatively simple sample size calculations consultation with a biostatistician is recommended.