Marginal mean and 68% CL error bars on TT foreground parameters estimated when adopting different data choices for the Plik likelihood, in comparison with results from alternate approaches or models. We assume a ΛCDM model and always combine the Plik likelihood with a prior on τ = 0.07 ± 0.02 (we do not use low-ℓ temperature or polarization data here). “Plik TT+tauprior” indicates the baseline (HM, ℓ_min = 30, ℓ_max = 2508), while the other cases are described in Sect. 4.1. The grey bands show the standard deviation of the expected parameter shift, for those cases where the data used are a sub-sample of the baseline likelihood (see Eq. (53)).