Polarized synchrotron spectral index as a function of the absolute value of latitude for the Faraday-corrected data (RM-SPASS). Regions at the same latitude are combined by estimating the inverse-variance weighted mean. Only regions for which the Pearson correlation coefficient is r >  0.2 are included. The horizontal line shows the inverse-variance weighted mean values of all regions, β_tot = −3.24.