Rest-frame EW of broad Hα in units of angstrom as a function of optical continuum deficit at 5100 Å given the broad Hα luminosity, represented by log ($L_{5100}^{\mathrm{obs}}/L_{5100}^{\mathrm{H}\alpha }$). The dotted line indicates the empirical L₅₁₀₀ − L(Hα^B) relation by Greene & Ho (2005) for SDSS AGN at z < 0.35. The dashed line and the shaded area show log ($L_{5100}^{\mathrm{obs}}/L_{5100}^{\mathrm{H}\alpha })=0.22$, updated by data for luminous quasars at z = 6 − 7 and the 68% interval of posterior predictives, respectively.