  A sample of 67 Broad Absorption Line quasars (BALQSOs) from the Large Bright
Quasar Survey (LBQS) is used to estimate the observed and intrinsic fraction of
BAL quasars in optically--selected samples at intermediate (B_J \simeq 18.5)
magnitudes. The observed BALQSO fraction in the redshift range 1.5 < z < 3.0 is
15\pm3%. A well--determined, empirical, k--correction, to allow for the
differences in the spectral energy distributions of non--BALQSOs and BALQSOs
shortward of \simeq 2100A in the restframe, is applied to the sample. The
result is an estimate of the intrinsic fraction of BALQSOs, in the redshift
range 1.5 < z < 3.0, of 22+/-4%. This value is twice that commonly cited for
the occurrence of BALQSOs in optically--selected samples and the figure is in
reasonable agreement with that from a preliminary analysis of the SDSS Early
Data Release. The fraction of BALQSOs predicted to be present in an optical
survey with flux limits equivalent to that of the FIRST Bright Quasar Survey
(FBQS) is shown to be \simeq 20%. The BALQSO fractions derived from the FBQS
and the LBQS suggest that optically--bright BALQSOs are half as likely as
non-BALQSOs to be detectable as S_1.4GHz > 1mJy radio sources.
