Type I quasar distance modulus (blue points) from a fit of Eq. (2) when assuming ΛCDM cosmology. The red points and bars (upper panel) are distance modulus averages and the standard deviations of the mean in small redshift bins. The purple line shows a flat ΛCDM model fit with Ω_m = 0.3; the dotted line is the reference distance modulus and its value is 46.5. The lower panel shows the residuals of the distance modulus at different redshifts.