REW_CIV as a functionof for different samples. The WISSH QSOs are indicated by blue and red stars, for the [OIII] and Weak [OIII] sample respectively.The BAL WISSH QSOs are indicated with black circles. Contours levels (0.03, 0.1, 0.5, and 0.9 relative to the peak) refer to the SDSS DR7 sample from Shen et al. (2011). The green diamonds indicate the PG QSOs from Baskin & Laor (2005) and Tang et al. (2012). The orange circles refer to the sample of WLQs from Plotkin et al. (2015), Luo et al. (2015), and Wu et al. (2011), the brown crosses indicate the HE QSOs from Sulentic et al. (2017), the ERQs from Hamann et al. (2017) are indicated with purple triangles. The purple dashed line marks the REW_CIV = 10 Å, which is the threshold for the WLQs. The distribution of the REW_CIV and are on the right and on the bottom, respectively.