Singular values of the arbitrary Mueller matrix are determined to be indicators of some polarization properties of the medium such as depolarization and diattenuation. Whereas eigenvalue analysis of the coherency matrix may wrongly characterize media with simultaneous strong depolarization and diattenuation effects. The comparison between the patterns of changes in singular-value and eigenvalue trends of the coherency matrix in experimental Mueller matrices, shows that singular values of the Mueller matrix are more capable of discriminating media with close degrees of depolarization.