Illustration of the robustness of the estimators against the unknown ψ₀ parameter when the covariance matrix departs from the canonical value. The covariance matrix is set up with ε_eff = 2 and a S/N p₀/σ_p,G = 1, and a true polarization fraction p₀ = 0.1. For each value of ψ₀, we first illustrate (in the left-hand panel) the performance of the seven estimators on one particular measurement set to the maximum of the PDF. We focus then on the statistical average estimates computed over 10 000 Monte-Carlo realizations for each value of the polarization angle for the naïve, MAS, and MB estimators (right-hand panel), where the full lines stand for the mean, and the dot-dashed lines for the 1σ dispersion.