Top: amount of global attenuation in the GRBH in the V band as a function of the amount of extinction in the V band along the GRB l.o.s. Middle: colour excess for the stellar continuum as a function of the colour excess for the Balmer lines. The grey line represents the C00 relation. Bottom: amount of attenuation of the Balmer lines in the V band as a function as the amount of extinction in the V band along the GRB l.o.s. For all panels the grey dash-dotted line represents the best fit using an orthogonal distance regression (using SciPy’s scipy.odr) and the grey shaded area its 1σ uncertainty. The χ², number of degrees of freedom and Null Hypothesis Probability (NHP) of these fist are indicated.