Distribution of recovered values of β and σ_v from mock catalogues. Each blue point in the bottom left panel gives the best-fitting values of β and σ_v for the combination of two VIPERS-like mock fields. The histogram in the top panel shows the PDF of the recovered values of β and the bottom right panel gives the PDF of the recovered values of σ_v. The grey band is the expected value of β given the fiducial cosmology and the uncertainty on the bias.