  Radio-selected samples of quasars with complete optical identifications offer
an ideal dataset with which to investigate dust bias associated with
intervening absorption systems. Here, we review our work on the Complete
Optical and Radio Absorption Line System (CORALS) survey whose aim is to
quantify this bias and assess the impact of dust on absorber statistics. First,
we review previously published results on the number density and gas content of
high column density absorbers over the redshift range 0.6 < z < 3.5. We then
present the latest results from CORALS which focus on measuring the metal
content of our unbiased absorber sample and an investigation of their
optical--IR colours. Overall we find that although dust is unarguably present
in absorption galaxies, the level appears to be low enough that the statistics
of previous magnitude limited samples have not been severely affected and that
the subsequent reddening of background QSOs is small.
