  Using UMRAO centimeter-band total flux density and linear polarization
monitoring observations of the complete Pearson-Readhead extragalactic source
sample obtained between August 1984 and March 2001, we identify the range of
variability in extragalactic objects as functions of optical and radio
morphological classification, and relate total flux density variations to
structural changes in published coeval VLBI maps in selected objects. We have
identified preferred orientations of the electric vector of the polarized
emission at 14.5 and 4.8 GHz in roughly half of the objects, and compared these
with orientations of the flow direction indicated by VLBI morphology. When
comparing the distributions of the orientation offsets for the BL Lacs and for
the QSOs, we find differences in both range and mean value, in support of
intrinsic class differences. In the shock-in-jet scenario, we attribute this to
the allowed range of obliquities of shocks developing in the flow relative to
the flow direction. The fact that we find longterm stability in EVPA over many
events implies that a dominant magnetic field orientation persists; in the
core-dominated objects, with small contribution from the underlying quiescent
jet, this plausibly suggests that the magnetic field has a longterm memory,
with subsequent shock events exhibiting similar EVPA orientation, or,
alternatively, the presence of a standing shock in the core. We have looked for
systematic, monotonic changes in EVPA which might be expected in the emission
from a precessing jet, a model currently invoked for some AGNs; none were
identified. Further, we carried out a Scargle periodogram analysis of the total
flux density observations, but found no strong evidence for periodicity in any
of the sample sources.
