  Modified gravity theories generically predict a violation of Lorentz
invariance, which may lead to a modified dispersion relation for propagating
modes of gravitational waves. We construct a parametrized dispersion relation
that can reproduce a range of known Lorentz-violating predictions and
investigate their impact on the propagation of gravitational waves. A modified
dispersion relation forces different wavelengths of the gravitational wave
train to travel at slightly different velocities, leading to a modified phase
evolution observed at a gravitational-wave detector. We show how such
corrections map to the waveform observable and to the parametrized
post-Einsteinian framework, proposed to model a range of deviations from
General Relativity. Given a gravitational-wave detection, the lack of evidence
for such corrections could then be used to place a constraint on Lorentz
violation. The constraints we obtain are tightest for dispersion relations that
scale with small power of the graviton's momentum and deteriorate for a steeper
scaling.
