Recent advances in establishing the nature and scope of estimators in
econometrics have shed more light on the importance of instrumental
variables. In this book, the authors argue that such methods may be
regarded as a strong organizing principle for a wide variety of
estimation and hypothesis testing problems in econometrics and
statistics. In support of this claim they present and develop the
methodology of instrumental variables in its most general and
explanatory form. They show, for instance, that techniques commonly used
to handle simultaneity and related problems can be reduced to one of two
generic variables of instrumental variables estimators, allowing them to
explore further the conditions under which different proposed estimators
are efficient.