  We present a unified formalism describing EPR test using spin 1/2 particles,
photons and kaons. This facilitates the comparison between existing experiments
using photons and kaons. It underlines the similarities between birefringence
and polarization dependent losses that affects experiments using optical fibers
and mixing and decay that are intrinsic to the kaons. We also discuss the
limitation these two characteristics impose on the testing of Bell's
inequality.
