(Color online) a) Likelihood distribution functions for De Filippis et al. (2005) sample. The solid and the dotted blue lines are likelihood functions corresponding to linear and non-linear η(z) parametrizations for the isothermal elliptical β model. The dashed and the dashed-dotted red lines are likelihood functions corresponding to linear and non-linear parametrizations for the isothermal spherical β model. b) The likelihood distribution functions for Bonamente et al. (2006) sample. The solid blue line and the dotted red line correspond to linear and non-linear parametrizations.