The PDF of the density contrast, measured around each galaxy in the current zCOSMOS 10k catalogue as discussed in the text (histogram). The solid line and shaded area correspond, respectively, to the mean and 1σ dispersion of the same statistics, measured on the 24 Millennium mocks; the dashed curve gives instead, as reference, the expected theoretical distribution for a lognormal model in a ΛCDM cosmology with (Ω_m, Ω_Λ, σ₈) = (0.25, 0.75, 0.8), at the mean redshift of the 10k sample, computed as discussed in the text. The vertical solid lines correspond to values of the density contrast excluding the top 5, 10 and 15 per cent of the distribution.