We present a theoretical study on differential group-delay (DGD) statistics
for common models of polarization-mode dispersion (PMD) emulators. Our stu
dy will show, for the first time to our knowledge, that the statistics for
the length of the PMD vector will not necessarily behave as a system with t
hree degrees of freedom when the number of sections in the PMD emulator is
low. However, when the number of sections is Large, i,e,, 10 sections or mo
re, the length of the PMD vector is well described with a system with three
degrees of freedom.