The design of an experiment using statistical power with a startle chamber study as an example

Using a startle chamber experiment as a case study, it is shown how the sensitivity of a study's design can be quantified by using the concept of statistical power and how the design can be planned to achieve the power desired. The purpose of the experiment was to compare background responses in three empty startle chambers. The study design nested groups of noise events into trials, entailing two sources of experimental error, variation within trials and between trials. For this nested design, the proper statistical analysis and calculation of power are described. It is shown how the power depends on the numbers of trials and events per trial (sampling effort), magnitudes of the sources of variability and background differences to be detected. A worked example shows the power associated with several sampling alternatives. Associated implications for cost and benefit are also discussed.