Quasars found in low frequency radio surveys are often assumed to have their jet axes randomly oriented in the sky because relativistically beamed radio cores rarely contribute significantly to the total flux density at metrewaves. But an orientation bias can still arise from the optical magnitude limit of the sample (Kapahi & Shastri 1987) if radio beaming is accompanied by an enhancement of the optical continuum as well (due to beaming or other effects). Such a bias can explain the finding (de Ruiter et al. 1986) that the typical value of R (ratio of core to extended flux density at 5 GHz) for the magnitude limited Bologna sample is about 5 times larger than for 3CR quasars, eventhough both samples are from low frequency surveys. It is thus consistent with the unified scheme for quasars (Orr & Browne 1982; Kapahi & Saikia 1982), which in fact requires an aspect dependence of the optical continuum (eg. Browne & Wright 1985; Browne & Murphy 1987).