One-Sided or Two-Sided ρ-Values: Which Most Appropriately Address the Question of Drug Efficacy?

Whether a one-sided or a two-sided ρ value should be used for reporting the results of an analysis should be determined by the a priori question the investigation seeks to answer. It is concluded that one-sided ρ values are appropriate in clinical trials whose objective is to provide definitive, confirmatory evidence of efficacy of pharmaceutical compounds.