Distribution of the Galactocentric distances of our APOGEE sample. Grey bars indicate bulge stars (according to the left vertical scale), while the blue and red open histograms show the thick and the thin disc (according to the right vertical scale), respectively. The vertical dashed line defines our cut at R_GC = 3.5 kpc to select likely bulge stars, while the vertical dotted line represents our cut at R_GC = 7.7 kpc used to select the comparison disc sample (see Sect. 6).