Power Calculations and Sample Size Determination

Abstract

Another method of determining sample sizes is based on power when testing a hypothesis. For example, when comparing the means for two groups, one way of determining sample size based on the power of recognizing a certain size of difference in the means. A sample size is determined that will allow that difference to be detected with high probability. Using power to determine sample sizes is especially useful when some important analytic comparisons can be identified in advance of selecting the sample. Although not covered in most books on sample design, most practitioners will inevitably have applications where power calculations are needed. R code from the stats package and specialized functions in the PracTools package are used in the examples.