This paper deals with the estimation of parameters involved in the classical steady-state modelling of network elements within the context of power system state estimation. A general method is proposed for the identification and correction of the real-time data, based on the sensitivity relationship between the measurement residuals and the parameter error; this relationship is treated as an estimation problem, yielding a parameter error estimate. Special emphasis is put on the real-time correction of erroneous transformer tap positions, the most frequent parameter errors during the real-time operation of state estimators. The proposed method is very simple and efficient, since it merely requires a single substitution in the state estimation linear system. Relationships with other methods are also discussed. Simulation results on a real-life system are reported.