Metallicity-sensitive line intensity ratios as a function of bolometric luminosity for the sample of Shin et al. (2013; gray squares) and the GTC sample (black circles). Open symbols are for population B sources, filled symbols for population A. The ordinate of the top panel is the decimal logarithm of the intensity ratio between Nvλ1240 and Civλ1549; the ordinate of the bottom panel is the decimal logarithm of the intensity ratio of the 1400 Å blend due to multiplets of SiIV and OIV], and Civλ1549. The dashed lines show the value expected for 0.2, 1, and 10 times solar metallicity following the LOC models reported in Nagao et al. (2006b).