Relation of SFE and the dense gas measures of individual clouds. Light blue shows clouds with R_Gal < 7.5 kpc kpc. The symbol size corresponds to the cloud area > 3 mag. Left: using the dense gas mass fraction, f_DG, measured using two column density thresholds, mag and mag. The line shows a fit with a = 0.6 ± 0.2, similar to the relation found previously for nearby molecular clouds (e.g. Kainulainen et al. 2014). Right: using the relative density contrast, ΔA_V. The line shows the fit of SFE ∝ 10^aΔA_V with a = 1.7 ± 0.4.