  (Abridged) We present a comprehensive study of the relation between radio and
X-ray emission in neutron star X-ray binaries, use this to infer the general
properties of the disc-jet coupling in such systems, and compare the results
quantitatively with those already established for black hole systems. There are
clear qualitative similarities between the two classes of object: hard states
below about 1% of the Eddington luminosity produce steady jets, while transient
jets are associated with outbursting and variable sources at the highest
luminosities. However, there are important quantitative differences: the
neutron stars are less radio-loud for a given X-ray luminosity (regardless of
mass corrections), and they do not appear to show the strong suppression of
radio emission in steady soft states which we observe in black hole systems.
Furthermore, in the hard states the correlation between radio and X-ray
luminosities of the neutron star systems is steeper than the relation observed
in black holes by about a factor of two. This result strongly suggests that the
X-ray emission in the black hole systems is radiatively inefficient, with an
approximate relation of the form L_X \propto \dot{m}^2, consistent with both
advection-dominated models and jet-dominated scenario. On the contrary the jet
power in both classes of object scales linearly with accretion rate. This
constitutes some of the first observational evidence for the radiatively
inefficient scaling of X-ray luminosity with accretion rate in accreting black
hole systems.
