  We present the system equivalent flux density (SEFD) expressions for all four
Stokes parameters: I, Q, U, V. The expressions were derived based on our
derivation of SEFD I (for Stokes I) and subsequent extensions of that work to
phased array and multipole interferometers. The key to the derivation of the
SEFD Q, U, V expressions is to recognize that the noisy estimates of Q, U, V
can be written as the trace of a matrix product. This shows that the SEFD I is
a special case, where the general case involves a diagonal or anti-diagonal 2x2
matrix interposed in the matrix multiplication. Following this step, the
relation between the SEFD for I and Q, U, V becomes immediately evident. We
present example calculations for a crossed dipole based on the formulas derived
and the comparison between simulation and observation using the Murchison
Widefield Array (MWA).
