Comparison of the distribution of the galaxy membership counts (richness) for given mass and the prediction for Poissionian scatter (black curves). The mean masses in the interval are 10¹⁴ M_⊙ (red curve) and 4.5 × 10¹⁴ M_⊙ (blue curve), respectively. The curves show cumulative histograms normalised to unity. The data are taken from the GAEA F lightcone in the redshift interval z = 1.5 − 2.