  A unique set of UV-optical spectrograms of 22 low redshift QSOs are
investigated using principal component analysis. We find three significant
principal components over the broad wavelength range from Ly\alpha to H\alpha.
They together account for about 78% of the sample intrinsic variance. We
present strong arguments that the first principal component represents the
Baldwin effect, relating equivalent widths to the luminosity (i.e. accretion
rate), but only emission-line cores are involved. The second component
represents continuum variations, probably dominated by intrinsic reddening. The
third principal component directly relates QSO UV properties to the optical
principal component 1 found by Boroson & Green (1992). It is the primary cause
of scatter in the Baldwin relationships. It is also directly related to broad
emission-line width and soft X-ray spectral index, and therefore probably
driven by Eddington accretion ratio. We demonstrate how Baldwin relationships
can be derived using our first principal component, virtually eliminating the
scatter caused by the third principal component. This rekindles the hope that
the Baldwin relationships can be used for cosmological study.
