Figure 5: Median, mean, and of fractional polarization for flat- (a) and steep-spectrum (b) sources. Black points refer to the almost complete subsample of the AT20G survey with  mJy for flat-spectrum sources and 300 mJy for steep-spectrum sources. Red points refer to data presented in [39]. Green points refer to the B3-VLA sample (with respect to [46], we distinguish flat- and steep-sources on the basis of their spectral index between 1.4 and 5 GHz; values shown in the plot are obtained using the ASURV code, taking into account upper limits in the fractional polarization). Cyan points refer to the sample from [50] (see text and Table 2; empty cyan points at 43 GHz for the steep-spectrum have to be considered as upper limits). Blue points refer to results from [51] and magenta points from [49] (solid and empty points are for FSRQs and BL Lacs, resp.). Yellow points refer to the NVSS survey (see [16]): for steep-spectrum sources we plot results for sources with mJy and  mJy.