Top panel: Mass-metallicity relation considering different planetary mass ranges. Orange and blue lines show the best fit for the fully mixed (FM) and core+envelope (CE) cases when considering planets of masses between only 0.2 and 2 M_J. The shaded areas show the 1σ error contour. The relations previously obtained (see Sect. 4) when considering the full range of planetary masses (from 0.1 to 10 M_J) are shown with dotted lines. The metallicities of Jupiter and Saturn are shown in black. Bottom panel: Mass-metallicity relation considering different precision on observed radius. Orange and blue lines show the best fit for the fully mixed (FM) and core+envelope (CE) cases when only considering planets with relative uncertainties on radii which are less than 3%. The previously obtained relations, shown with dotted lines, include planets with an uncertainty on radius of up to 8%.