[Fe/H] values from the literature estimates versus the values obtained in this work. Upper panel: differences between the metallicities given in the literature and those derived in this work. Median uncertainties in the derived metallicities are also shown. The symbol ⟨⟩ in the legend represents the median difference. The black continuous line represents the 1:1 relation, whilst the grey dashed one represents the best linear fit between our estimates and those obtained using the relationship reported by NE12 (see text in Sect. 4.2).