Histograms of the fractional differences between coadded and SE C IV emission line width measurements, FWHM (left) and σ_l (right). The histograms are color-coded by data quality as shown in the legend (note: the S/N < 5 subsample is contained within the S/N < 10 subsample). The similarly color-coded shaded bars in the small top panels show the asymmetric scatter, given by the 16th–84th-percentile range, of each data-quality distribution, and the points and arrows correspond to the distribution median ± the median fractional statistical uncertainty given in column 5 of Tables 1 and 2, respectively. An increasing bias is seen for lower-S/N subsamples that, while encompassed within the scatter of all distributions, is also encompassed within the statistical uncertainties at all S/N levels for σ_l but only for S/N > 10 for the FWHM.