  In a recent paper, Schutz proposed an analytical approximation for
simplifying treatment of polarization angle and conveniently evaluating
relative detection rates of compact binary inspirals for various networks of
ground-based interferometers. We derived relative event rates by strictly
handling polarization angle and quantitatively examine validity of Schutz's
approximation. The associated error of the approximation is rigorously shown to
be less than 1.02\%, irrespective of details of the detector networks.
