Histograms of χ² for the Planck 2015 Commander (red), NILC (orange), SEVEM (green), and SMICA (blue) foreground-cleaned maps analysed with the common mask. The χ² is obtained by combining the three MFs in needlet space with an appropiate covariance matrix. The histograms are for the FFP8 simulations, while the vertical lines are for the data. The figures from left to right are for the needlet scales j = 4,6, and 8, with the central multipoles ℓ_c = 2^j shown in each panel.