Left: likelihood distribution functions from the De Filippis et al. (2005) and Union2 SN Ia pairs for two parameterizations: η( z) = 1 + η ₀ z and η( z) = 1 + η ₀ z/(1 + z). Right: likelihood distribution functions from the Bonamente et al. (2006) and Union2 SN Ia pairs for the same parameterizations. The top and bottom panels correspond to the cases without and with the errors of SNe Ia, respectively.