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Determining black hole masses and accretion rates with better accuracy andprecision is crucial for understanding quasars as a population. These arefundamental physical properties that underpin models of active galactic nuclei.A primary technique to measure the black hole mass employs the reverberationmapping of low-redshift quasars, which is then extended via theradius-luminosity relationship for the broad-line region to estimate massesbased on single-epoch spectra. An updated radius-luminosity relationshipincorporates the flux ratio of optical Fe ii to H$\beta$ ($\equiv\mathcal{R}_{\rm Fe}$) to correct for a bias in which more highly accretingsystems have smaller line-emitting regions than previously realized. In thiscurrent work, we demonstrate and quantify the effect of using this Fe-correctedradius-luminosity relationship on mass estimation by employing archival datasets possessing rest-frame optical spectra over a wide range of redshifts. Wefind that failure to use a Fe-corrected radius predictor results inoverestimated single-epoch black hole masses for the most highly accretingquasars. Their accretion rate measures ($L_{\rm Bol}/ L_{\rm Edd}$ and$\dot{\mathscr{M}}$), are similarly underestimated. The strongest Fe-emittingquasars belong to two classes: high-z quasars with rest-frame optical spectra,which given their extremely high luminosities, require high accretion rates,and their low-z analogs, which given their low black holes masses, must havehigh accretion rates to meet survey flux limits. These classes have masscorrections downward of about a factor of two, on average. These resultsstrengthen the association of the dominant Eigenvector 1 parameter$\mathcal{R}_{\rm Fe}$ with the accretion process.

Systematically smaller single-epoch quasar black hole masses using a radius-luminosity relationship corrected for spectral bias