EC peak luminosity in the observer's frame as a function of the beaming factor for PMN J0948+0022 and 1H 0323+342. The violet solid and red dotted lines are the best fits to the data by considering the errors in both X and Y axes. The data of 3C 279 with the best-fit line (black dashed line) are also shown for comparison. The data are from Zhang et al. (2013c).