Negative, anomaly-free, oblique radiative corrections

Current electroweak precision measurements tend to prefer negative values of the oblique radiative parameters, S and T, relative to their standard-model expectations. This tendency is shown to be consistent with the existence of new colorless fermions in the anomaly-free combination of two doublets (${\mathit{N}}_1$,E${)}_{\mathit{L}}$ and (${\mathit{E}}^{\mathit{c}}$,${\mathit{N}}_2$ ${)}_{\mathit{L}}$ and one singlet ${\mathit{N}}_{3\mathit{L}}$, which are contained in some supersymmetric or ${\mathit{E}}_6$ extensions of the standard model.