Δα_ox (left) and photon index Γ_X (right) as a function of the rest frame C IV EW for the z ≃ 3 and T20/C IV samples. The Δα_ox values for the z ≃ 3 sample have been adjusted to be consistent with T20 (see text for details). The solid line in the left panel is the Δα_ox–C IV EW relation reported by T20 (see their Eq. (4)). X-ray-weak quasars in T20 (Δα_ox ≤ −0.2) are marked with brown open circles.