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We review the basic techniques for extracting information about quasarstructure and kinematics from the broad emission lines in quasars. We considerwhich lines can most effectively serve as virial estimators of black hole mass.At low redshift the Balmer lines,particularly broad H beta, are the lines ofchoice. For redshifts greater than 0.7 - 0.8 one can follow H beta into the IRwindows or find an H beta surrogate. We explain why UV CIV 1549 is not a safevirial estimator and how MgII 2800 serves as the best virial surrogate for Hbeta up to the highest redshift quasar known at z ~ 7. We show how spectralbinning in a parameter space context (4DE1) makes possible a more effectivecomparison of H beta and MgII. It also helps to derive more accurate massestimates from appropriately binned spectra and, finally, to map the dispersionin black hole mass and Eddington ratio across the quasar population. FWHM MgIIis about 20% smaller than FWHM H beta in the majority of type 1 AGN requiringcorrection when comparing black hole mass estimates from these two lines. The20% of sources showing narrowest FWHM H beta (< 4000 km/s) and strongest FeII(R_FeII >~ 1.0) emission (we call them bin A3-4 sources) do not show this FWHMdifference and a blueshift detected in MgII for these sources suggests thatFWHM H beta is the safer virial estimator for these extreme Eddington emitters.

Techniques for Profile Binning and Analysis of Eigenvector Composite Spectra: Comparing Hbeta and MgII 2800 as Virial Estimators