Posterior probability distribution of the model. Parameters shown: average log M₅ and γ at fixed stellar mass and half-light radius, and intrinsic scatter around the average. Filled contours: model describing SLACS lenses, without correction for selection effects (see Section 4.8). Thick solid curves: fiducial model. Thin solid curves: model with no fundamental plane prior of Equation (37). Contour levels correspond to 68% and 95% enclosed probability.