Isotropy and polarization in a statistically stationary electromagnetic field in three-dimensions

A parameter, called the degree of isotropy, used in conjunction with the degree of polarization defined by Ellis, Dogariu, Ponomarenko and Wolf (Opt. Commun. 248 333 (2005)) in a recent paper, is shown to more completely characterize the state of a statistically stationary electromagnetic field in three dimensions. A simple expression is presented that relates the maximum degree of polarization to a given degree of isotropy, and a simple graphical representation of a state is given that clearly shows where the state stands among all possible states.