  Statistical investigations of samples of quasars have established that
clusters of properties are correlated. The strongest trends among the
ultraviolet emission-line properties are characterized by the object-to-object
variation of emission from low-velocity gas, the so-called ``intermediate-line
region'' or ILR. The strongest trends among the optical emission-line
properties are characterized by the object-to-object variation of the line
intensity ratio of [O III] 5007 to optical Fe II. Additionally, the strength of
ILR emission correlates with [O III]/Fe II, as well as with radio and X-ray
properties. The fundamental physical parameter driving these related
correlations is not yet identified. Because the variation in the ILR dominates
the variation in the equivalent widths of lines showing the Baldwin effect, it
is important to understand whether the physical parameter underlying this
variation also drives the Baldwin effect or is a primary source of scatter in
the Baldwin effect.
