The number of QSOs included in available complete samples already exce
eds 1600. We evaluate their three- and four-point correlation function
s and obtain 0.15 +/- 0.05 less than or equal to Q less than or equal
to 1.30 +/- 0.37 and Q((4)) less than or equal to 4.9 +/- 1.9, respect
ively. The available fair samples are still the sum of a number of dis
connected areas. Inside all of them the average distance between nearb
y QSOs widely exceeds the correlation distance. As a consequence of th
is low density, the values allowed for Q and Q((4)) are quantized, alt
hough the quantized levels depend on the characteristics of each conne
cted subsample area. We give a quantitative evaluation of how denser a
nd wider the connected subsamples should be, in order that limits on n
-point functions can be substantially improved and apparent quantizati
on effects can be overcome.