Projection effects in the determination of HOD by the background subtraction method. The dotted line shows the HOD of groups that have, in projections, other groups in the characteristic radius; the dashed line corresponds to the HOD of groups without contamination; and the solid line is the HOD of all groups. A standard jackknife procedure is applied to estimate errors. For the sake of clarity we only plot the results corresponding to M_lim = −19.0. The bottom panel shows the quotient between the HOD estimated with and without contamination and the HOD of all groups.