The Physics of Blazar Optical Emission Regions II: Magnetic Field   Orientation, Viewing Angle and Beaming
  For a sample of 51 blazars with extensive optical polarization data, we used circular statistics to calculate the scatter among the polarization position angles for each object. We found that this scatter is correlated with the radio core dominance. We compared this relationship with the predictions of a simple transverse shock model. The result suggests that blazar jets are likely to cover a wide range of speeds consistent with those derived from observations of superluminal motion. 
Michael J. Yuan, Hien Tran, Beverley Wills, D. Wills