  In 1998, A. Karimi and I.D. Landau published in the journal "Systems and
Control letters" an article entitled "Comparison of the closed-loop
identification methods in terms of bias distribution". One of its main purposes
was to provide a bias distribution analysis in the frequency domain of
closed-loop output error identification algorithms that had been recently
developed. The expressions provided in that paper are only valid for prediction
error identification methods (PEM), not for pseudo-linear regression (PLR)
ones, for which we give the correct frequency domain bias analysis, both in
open- and closed-loop. Although PLR was initially (and is still) considered as
an approximation of PEM, we show that it gives better results at high
frequencies.
