Constraints on α coming from published analyses of several sets of CMB experimental data sets (shown in grey) as reviewed in Kaufman et al. (2016) compared with what is found in the present paper (in blue). For each experiment the left error bars are for statistical uncertainties at 68% CL, while right error bars (when displayed) are obtained by summing linearly the statistical and systematic uncertainties. The error bar of BOOM03 already contains a contribution from systematic effects.