Mean (x-axis) and standard deviation (y-axis) for the estimated values of E_b (upper panel) and δ (lower panel). In the upper panel, galaxies with a secure (>2σ) detection of the bump are located to the right side of the solid line. In the lower panel, galaxies with an attenuation curve confirmed to be steeper than the Calzetti one are located to the left side of the solid line (see text for details). The symbols are the same as in Fig. 3.