Top panel: relation between R(NII) = [NII]λ5755/(1.33⋅[NII]λ6584) and R(OII) = [OII]λλ7320, 7330/[OII]λλ3726, 3729, for our nitrogen sub-sample of 53 systems. Bottom panel: relation between T_e(NII) and T_e(OII) for the same nitrogen sub-sample. These two temperatures are expected to be roughly the same for a given HII region, as indicated by the line of equality (dashed line). Points with grey outlines (in both panels) are outliers with T(OII) > T(NII) + 2000 K, or equivalently, R(OII) > R(NII) + 0.0175.