Results of our four-parameter fits: the evolution of the slope of the radial metallicity gradient between 6 and 13 kpc (top panel), the mean metallicity at R_Gal = 6 kpc (second panel), the mean metallicity at R_Gal = 12 kpc (third panel), the slope of the [Fe/H] scatter with Galactocentric radius (fourth panel), and the [Fe/H] scatter in the solar annulus (bottom panel), for the datasets considered here (error bars). The black line and the shaded bands around it correspond to the bias-corrected CoRoGEE measurements, their statistical uncertainties, and the systematic uncertainties stemming from the bias correction. The fit for the full MCM model did not converge in the last age bin.