Relative attenuation probed by Balmer lines. The first row shows the results obtained by fitting a linear function to the log(Hα/Hγ/2.86×0.469) vs. log(Hα/Hβ/2.86) relation within each 3D bin we defined. From left to right, we plot the distributions of the slope, intercept, and the intrinsic scatter. For each distribution, we show the 68% confidence interval of the median [CI(Mdn)] and the standard deviation (SD). The dashed-red lines indicate the median values among our 3D bins. The dashed-green lines indicate the values obtained by the traditional method where the whole sample is used for a single fit. The dashed-blue lines correspond to the values given by the F99 extinction curve. The second row shows similar information, but is obtained by fitting a linear function to the log(Hα/Hδ/2.86×0.259) versus log(Hα/Hβ/2.86) relation.