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We try to identify the sources and systematics of the uncertainty of themasses of the central black holes in active galactic nuclei (AGNs) which havebeen obtained by reverberation-mapping methods. We characterize the broadH$\beta$ emission-line profiles by the ratio of their full-width at halfmaximum (FWHM) to their line dispersion, i.e., the second moment of the lineprofile. We use this parameter to separate the reverberation-mapped AGNs intotwo populations, the first with narrower H$\beta$ lines with relativelyextended wings, and the second with broader lines that are relativelyflat-topped. The first population is characterized by higher Eddington ratiosthan the second. Within each population, we calibrate the black-hole mass scaleby comparison of the reverberation-based mass with that predicted by the bulgevelocity dispersion. We also use the distribution of ratios of thereverberation-based mass to the velocity-dispersion mass prediction in acomparison with a ``generalized thick disk'' model in order to see ifinclination can plausibly account for the observed distribution. We find thatthe line dispersion is a less biased parameter in general than FWHM for blackhole mass estimation, although we show that it is possible to empiricallycorrect for the bias introduced by using FWHM to characterize the emission-linewidth. We also argue that inclination effects are apparent in a small subset ofobjects with the narrowest emission lines. Our principal conclusion is that theH$\beta$ profile is sensitive primarily to Eddington ratio, but thatinclination effects play a role in some cases. (abridged)Comment: 19 pages, 11 figures, accepted in A&

Systematic effects in measurement of black hole masses by emission-line reverberation of active galactic nuclei: Eddington ratio and inclination