The contrast parameters associated with the generalized Stokes vector in a Young's interference experiment are analyzed. It is shown that there are two unitary transformations that can be applied to the electric fields so that a partially polarized light can be described with no more than two non-zero generalized Stokes parameters. Furthermore, general conditions are derived which indicate when totally unpolarized light can be described with only one non zero generalized Stokes parameter after unitary transformations.