This paper surveys J. D. Sargan's work on instrumental variable estimation and its connections with the generalized method of moments. I first present the modelling context in which Sargan motivated instrumental variable estimation. Then I review the theory of instrumental variable estimation as...

We develop methods for testing the hypothesis that an econometric model is underidentified and inferring the nature of the failed identification. By adopting a generalizedmethod of moments perspective, we feature directly the structural relations and we allow for nonlinearity in the econometric...