Two-dimensional plot of the raw likelihood (posterior distribution) as a function of dark energy spectral index n_de and the transformed amplitude , using WMAP 7-yr data. The spherical angles have been fixed to their WMAP best fit values at ℓ_max = 20 to enable a projection. The posterior mode value is located at n_de = 3.1. The (transformed) amplitude found in this plot is higher than the value for the true anisotropic amplitude noted in Table 1 due to a bias introduced by application of the mask and a linear transformation.