Balmer decrements for our sample relative to the theoretical Case B recombination values for T_e = 11 400 K. The solid lines represent four different extinction laws as shown for a range of Δ A_V = 1.4 mag. Points in gray are for the whole sample, while points in blue correspond to objects with errors in both axes < 0.015. The black cross at the bottom left represents the mean error of the whole sample.