Top panel: mass ratio of silicate and carbon dust versus the constant term c₁ of Eq. (2) in observations of the extinction curve between 115–330 nm (Valencic et al. 2004; Gordon et al. 2009). Mid panel: mass ratio of very small (r < 6 nm) and large grains versus the parameter c₃ of Eq. (2); the parameter c₃ describes the strength of the extinction bump. Bottom panel: mass ratio of very small (r < 6 nm) and large grains versus the parameter c₄ of Eq. (2), which describes the strength of the far UV rise. The L-sample is shown with open circles and the L_S -sample with grey filled circles together with their Pearson coefficient (black). Single-cloud sight-lines (red squares) with 1σ error bars and Pearson coefficient are shown in red. They are fit by straight lines employing the MLE (red solid line), PCA (green solid line), and minimum χ² (blue solid line) method.