DHO amplitude (σ _DHO) and emission-line properties. Left: distribution of quasars in the EV1 parameter space, with the color showing the mean σ _DHO of objects in the corresponding bins; a trend of increasing σ _DHO toward the upper left corner is clearly shown. Right: distribution of quasars in the C IV parameter space, with the color showing the mean σ _DHO of objects in the corresponding bins; a trend of increasing σ _DHO with decreasing C IV blueshift and increasing C IV EQW is shown.