  A statistical model is used to determine how stochastic fluctuations in the
intensities of orthogonal polarization modes contribute to the modulation and
depolarization of pulsar radio emission. General expressions for the
distributions of the Stokes parameters, linear polarization, polarization
position angle, and fractional polarization are derived when the mode
intensities follow the same or different probability distributions. The
transition between modes is examined. When the mode intensities follow the same
distribution, the fractional linear polarization and modulation index are
symmetric about the transition. The symmetry is disrupted when the mode
intensities follow different distributions. The fractional linear polarization
is minimum and the mode frequency of occurrence changes rapidly at transitions
where the mode intensity distributions are the same and the modulation index is
small. A lower limit on the fractional linear polarization that can be attained
via the simultaneous occurrence of the modes as a function of modulation index
is quantified.
