Sample Size Calculations

Simply the number of subjects included in a study determined by a calculation.

Click here to download a fact sheet on Sample Size Calculations at the bench.

What does it mean to calculate sample size?

The term sample size refers to the number of study subjects included in an experiment. Investigators generate this number by 1) coming up with a null and alternative hypothesis in line with the primary outcome of the study, 2) identifying appropriate variables (alpha, beta, measure of effect and variability) using literary evidence, expert opinion, or pilot studies, and 3) inputting these variables into an equation or the University of British Columbia Power and Sample Size Calculator.

Who should calculate sample size?

Just as clinical scientists calculate sample sizes to determine the number of trial participants needed for each experimental group, preclinical scientists are equally as responsible for calculating sample size. This is particularly important for ‘confirmatory’ experiments that will inform future directions and development of an intervention.

When should you calculate sample size?

Sample size should be calculated before the experiment begins. Similarly, determining the primary outcome of the experiment beforehand is important as this influences the sample size equation to be used as well as the variables to be inputted into the sample size equation.


Why calculate sample size?

By not calculating sample size ahead of time, you may be either a) including too many study subjects or b) including too few study subjects in the experiment, which would result in either a waste of time and resources or the generation of inaccurate results that are not reflective of the true population, respectively. It is also important to report the sample size and the variables used to calculate the sample size in the manuscript.


Optimal Practices

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