Editor,—The paper by Vic and colleagues1 provides useful pharmacokinetic data on the use of once daily aminoglycoside treatment in children with cystic fibrosis. However, their conclusions regarding efficacy and safety must be viewed with caution. They did not perform a power calculation and therefore they cannot exclude the possibility of a type 2 error—that is, one regimen may be more effective but insufficient patients have been studied to demonstrate this. In an equivalence study conventional tests of significance are inappropriate and the results should be expressed as a confidence interval wherein the true difference may lie.2

This study is also too small …