β_UV (1300 < λ/Å < 3000) and γ_opt (3000 < λ/Å < 10 000) distributions for the sample. Only the UV slope has been measured for the points along the constant line γ_opt = −1.5. Blue stars represent the values obtained from the lum-K13 template assuming E[B − V] values of 0, 0.05, and 0.1, and assuming observations in the UKIDSS YJHK bands plus W1 and W2 for QSOs at 5.5 ≥ z ≥ 7.5. The shaded light-blue areas delimit the 1 and 2σ confidence intervals for the luminous QSO subsample in Krawczyk et al. (2013).