Here's a good explanantion of the technical basis of the differences in power cords I stumbled across: http://www.AudioAsylum.com/audio/cables/messages/13538.html

As for determining my results, that's simple: listening. My ears are the final arbiter of the sonic differences between components, recordings, cables, vacuum tubes, phono cartridges, VTA adjustment, power conditioners, dampening / isolation devices and virtually every thing that goes into my system.