  Based on the most recent QSO ultraviolet spectra, the covering factor of the
clouds of the Broad Line Region (BLR) is about 30%, or larger. This value would
imply that in at least 30% of the QSOs our line of sight crosses one, or more,
BLR clouds and, in the latter case, the UV spectrum should show a sharp Ly-edge
in absorption. This Ly-edge in absorption is never observed. This paradox is
solved if, as suggested by various authors, the BLR is flattened and the dusty
gas in the outer parts, on the same plane, prevents the observation along the
lines of sight passing through the BLR clouds. The objects observed edge-on
(with respect to the flattened BLR) would be classified as obscured QSOs or,
within the framework of the unified model, type 2 QSOs. The covering factor of
the BLR constrains the fraction of obscured QSOs to be QSO2/QSO1 > 0.5. This
lower limit is already high with respect to the number of candidate type 2 QSOs
claimed so far. We discuss this constraint in relation to recent AGN surveys.
