The estimator of the coefficient covariance matrix proposed in White (1982) can be used to robustify the classical Wald test. Sampling experiments recently performed on linear regressions and simultaneous equation models, however, suggest that such an estimator tends to underestimate the...

The estimation method of Two Stage Least Squares (2SLS) with Principal Components (2SPC) is applied to a medium-sized nonlinear econometric model of the Italian Economy.