Linear stability theory is applied to analyze boundary-layer data from flow-control experiments with dielectric barrier discharge plasma actuators. The hydrodynamic stability of laminar boundary-layer flow along a flat plate subject to an adverse pressure gradient is enhanced by the induced momentum from a dielectric barrier discharge. Changes in the velocity distribution are measured with laser Doppler anemometry while a traversable hot-wire probe quantifies the macroscopic effect on the transition location. The observed connection between the altered velocity distribution and the delayed transition is supported by a stability analysis of experimental boundary-layer profiles. A numerical procedure to study the impact plasma actuation has on hydrodynamic stability is presented to enable parametric studies and optimization of flow-control applications.