Upper: comparison of the ΛCDM constraints on n_s (top-left) and single-parameter extensions of the ΛCDM model for a variety of data cuts for Planck+WP. Each sub-plot is obtained from a separate CosmoMC analysis of the corresponding model. The dashed lines show the results from Plik, an alternative likelihood discussed in Planck Collaboration XV (2014), run here with the same SZ and CIB foreground priors as for the CamSpec results. For the extended models, the value of the additional parameter in the base ΛCDM model is shown with the vertical dashed lines. Lower: same as the upper set of panels, but for Planck+WP+highL. Additional data from the high-ℓ CMB experiments significantly reduce the foreground degeneracies.