Observed number of γ-rays over number of events expected from the intrinsic spectra vs. γ-ray energy. The data sets are grouped by similar redshift and the detected and expected numbers of γ-rays are summed in each energy bin. The best fit EBL absorption is represented by the solid lines for the three redshifts corresponding to the groups of data sets and the shaded areas correspond to the  ± 1σ best fit EBL normalization.