used to interpret the observed evolution.

In general, the theoretical understanding of how matter clustering grows via gravitational instability in an expanding universe is presently quite well developed, even if the number of ingredients required in the models is large. As a consequence, it is relatively straightforward to compute the correlation function of matter fluctuations, $\xi_{\rm m}$, as a function of redshift, given a cosmological scenario \[see e.g. @pd96 [@smith03]\]. However, this does not lead directly to a prediction of QSO correlation properties because the details of the link between the distribution of active nuclei and the distribution of the mass are not fully understood. In principle, this relationship could be highly complex, non-linear and environment-dependent, making very difficult to obtain useful informations on the evolution of matter fluctuations from the AGN clustering. In this spirit, a relatively simple form of the local bias $b$ is generally assumed.

Matarrese et al. (1997; see also Moscardini et al. 1998; Hamana et al. 2001) developed an algorithm for describing the clustering on our past light-cone taking into account both the non-linear dynamics of the dark matter distribution and the redshift evolution of the bias factor. The final expression for the observed spatial 