We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity .
The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3 \leq z \leq 1.5 and an optical absolute magnitude range of -26.5 \leq M _ { B } \leq - 23.5 ( h , q _ { 0 } = 1 / 2 ) .
We have also matched up other existing surveys with the FIRST and NVSS radio catalogues and combined these data so that the optical luminosity-redshift plane is now far better sampled than previously .
We have fitted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift and from this model infer the radio-loud and radio-quiet optical luminosity functions .
The radio-loud optical luminosity function is featureless and flatter than the radio-quiet one .
It evolves at a marginally slower rate if quasars evolve by density evolution , but the difference in the rate of evolutions of the two different classes is much less than was previously thought .
We show , using Monte-Carlo simulations , that the observed difference in the shape of the optical luminosity functions can be partly accounted for by Doppler boosting of the optical continuum of the radio-loud quasars and explain how this can be tested in the future .