Median values (solid lines with symbols) and 95 per cent CIs (dotted lines with symbols) of D(α_int) for a mock dSph (large sample) generated with an Osipkov–Merritt velocity anisotropy. The true D(α_int) is given in solid black. The D-factor has been reconstructed using different anisotropy prescriptions: (i) constant (blue circles), (ii) Osipkov–Merritt (i.e. the correct parametrization, red triangles) and (iii) Baes and van Hese (green squares).