Relation between [O II] (left) and [S II] (right) auroral-to-strong line ratios differences and log(Hα/Hβ) from all the sub-bins, a total number of 1512. The line ratio differences mean the actual auroral-to-strong line ratios minus the intrinsic auroral-to-strong line ratios given by the intercept of the best-fit line in each bin. The purple contours represent the density distribution of data without any correction. The green contours represent data after a F99 correction with R_V = 3.1. The red contours represent data after our correcting method described in this section. The contour levels represent 68%, 95%, and 99% of all the data points. The dashed blue lines are horizontal. A horizontal distribution is expected for the correct attenuation correction, as there should be no residual dependence on the Balmer decrement.