The method of common-base proper orthogonal decomposition (CPOD) is introduced as a tool for processing data—numerical simulations or experiments—acquired over a selection of operating parameters, for the purpose of quantitative comparison and/or optimization. In the present work, a review of the standard proper orthogonal decomposition (POD) is presented to explain the need and the nomenclature of the new approach. In order to illustrate the capabilities of CPOD, both POD and CPOD are applied to spatial velocity fields obtained experimentally from immediately above dielectric barrier discharge plasma actuators operated in quiescent air.