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We have carried out a monitoring program to observe systematically the integrated total flux density and linear polarization of sources in the Pearson-Readhead sample of extragalactic objects at 4.8, 8.0, and 14.5 GHz. The large data base obtained has been used to investigate the statistical behavior of the flux and polarization in this well-defined sample and to search for dependence of these properties on other radio and optical properties. Variability is shown to be a nearly universal characteristic of BL Lac-type objects and QSOs at 14.5 GHz; at the lowest frequency, 4.8 GHz, the fraction of objects exhibiting variability and the amplitude of the variations are significantly reduced. Variability is correlated with a centimeter-wavelength spectral index and with VLBI structural compactness and, marginally, with redshift; but the average percentage polarization shows no correlation with these parameters. The time-averaged degree of linear polarization is related to VLBI morphology but shows little dependence on optical source classification. Intrinsic position angle orientations are compared with are compared with VLBI structural axes and with optical polarimetry data; while the number of BL Lac objects in the sample is small, the difference in both the shape and the peak value of the distribution of alignment difference is significantly different for BL Lac-type objects and QSOs suggesting that these objects are intrinsically different. Subject Headings: BL Lacertae objects: general - polarization - quasars: general - radio continuum: galaxies - surveys
Aller et al. (Sun,) studied this question.