  A sample of 103 quasars from the Large Bright Quasar Survey (LBQS) has been
observed with the VLA at 8.4 GHz to study the evolution of the radio luminosity
distribution and its dependence on absolute magnitude. Radio data from pointed
observations are now available for 359 of the 1055 LBQS quasars. The radio-loud
fraction is constant at ~10% over the absolute magnitude range -28 <= MB <=
-23, and it rises to ~20% (log R > 1) or ~35% (log L > 25) at the brightest
absolute magnitudes in the sample. This nearly flat distribution differs
markedly from those of the optically selected Palomar-Green (PG) Bright Quasar
Survey and the X-ray selected Extended Medium Sensitivity Survey (EMSS), both
of which have lower radio-loud fractions for absolute magnitudes fainter than
MB = -24 and higher fractions at brighter magnitudes. The reason for the high
radio-loud fraction at bright absolute magnitudes in the PG, compared to the
LBQS and other optically selected quasar surveys, is unknown. The trend of
increasing radio-loud fraction with absolute magnitude in the EMSS is due at
least in part to a correlation between X-ray and radio luminosity. Combining
the LBQS data with radio studies of high-redshift quasars leads to the
conclusion that the radio-loud fraction in optically selected quasars does not
appear to evolve significantly, aside from a modest increase at z ~1, from z =
0.2 to redshifts approaching 5, a result that is contrary to previous studies
which found a decrease in radio-loud fraction with increasing redshift by
comparing the low-z fraction in the PG to higher redshift samples.
