Linear fitting over the entire data set of [X/H] (left panel). The elements (right panel) are divided into three groups: α-elements (blue triangles), Fe-group elements (red diamonds), and other metals (purple circles). The blue dashed line shows linear fitting over solely the α-element abundances, the red solid line is the blue dashed line shifted to the value averaged over Fe-group elements. The gray filled areas show 3σ confidence intervals. The total metallicity [M/H]_tot is shown by intersection of gray dashed lines.