The relative densities (δ; see Section 3.2) of ALLSKY-only (right) and ALLWISE-only (left) selected quasars as a function of position. Blue indicates an underdensity relative to the mean, red is overdense. It is clear that the objects selected only by ALLSKY are less evenly distributed, suggesting that many are in fact artefacts or that there is a position-dependent bias affecting their selection. This is greatly reduced, but still present, in ALLWISE.