Histograms of polarization fraction (left) and dispersion of polarization angles (right) for all ALMA cores (dashed lines), and for all simulations (solid lines; with grain alignment via perfect alignment [PA] or radiative torques [RATs], and with or without filtering). The histogram lines have been smoothed with a 1D-Gaussian kernel of a size of 0.2% in and 2° in . In both panels, the shaded areas correspond to the mean of the uncertainty in and within each bin of the histogram. Right panel: we do plot the errors in , derived following Alina et al. (2016). We do not show uncertainties for the synthetically observed simulations, as they have not been filtered by the CASA simulator.