Eigenvector 1 Parameter Space: An H-R Diagram for the Quasars?

How does one go about finding an H-R Diagram for Quasars? Does it make any sense to search for one? We will review the evidence for phenomenological diversity among the broad-line emitting AGN that highlights the need for such a diagram. In other words, all quasars are not alike. We will then introduce a 4D parameter space that we call Eigenvector 1 which appears to provide optimal phenomenological discrimination between the major classes of AGN and that may also provide a framework for developing a unifying physical model.