Posterior probability of the parameters describing the distribution in velocity dispersion. These are defined in Equation (19) and Equation (20). Filled purple contours: Posterior probability of the model. Solid pink contours: Posterior predicted fundamental hyperplane of the SLACS lenses. Dashed black contours: Posterior predicted fundamental hyperplane of the SLACS lenses, based on the observed (noisy) velocity dispersion. The mean and standard deviation of the marginal posterior distribution in each parameter is indicated above the corresponding histogram. Contour levels indicate regions of 68% and 95% enclosed probabilities. The three points are values of the parameters obtained by means of dynamical modelling via the isotropic spherical Jeans equation, for different pairs of values of (α_sps, ϵ).