This paper does not attempt to correct for shortcomings of the traditional IV method but, rather, to develop a complementary method which can provide unbiased estimates under conditions where the IV method fails. The method relies on finding an auxiliary variable Z

For nearly a century, investigators in the social sciences have used regression models to deduce cause-and-effect relationships from patterns of association. Path models and automated search procedures are more recent developments. In my view, this enterprise has not been successful. The models tend to neglect the difficulties in establishing causal relations, and the mathematical complexities tend to obscure rather than clarify the assumptions on which the analysis is based. Formal statistical inference is, by its nature, conditional. If maintained hypotheses A, B, C,... hold, then H can be tested against the data. However, if A, B, C,... remain in doubt, so must inferences about H. Careful scrutiny of maintained hypotheses should therefore be a critical part of empirical work-- a principle honored more often in the breach than the observance.

Introduction It is common in the literature on instrumental variables to remark upon the difficulty of knowing or demonstrating that a potential instrument is exogenous, in the sense of being uncorrelated with the disturbances [Bartels, 1991, Johnston, 1972]. It is also widely recognized that exogeneity is an assumption embedded in the model specification [Engle, et al, 1984], hence, it rests on subjective judgment and, like other structural assumptions of causation and "zero-restrictions", it cannot be tested in purely observational studies. The purpose of this note is to show that despite its elusive nature, exogeneity can nevertheless be given some empirical test. The test is not guaranteed to detect all violations of exogeneity but it can, in certain circumstances, screen away real bad choices of would-be instruments. 2 An Instrumental Inequality Definition 2.1 (exogeneity) A variable z is said to be exogenous relative to an ordered

A central question in the study of democratic polities is the extent to which elite opinion about public policy shapes and potentially manipulates public opinion on those issues. Existing empirical estimates of the effect of elite communication on individual opinion formation are, however, characterized by a number of serious methodological problems, and consequently, there is little in the way of compelling evidence that elites actually influence individual opinions. This paper proposes an identification strategy for estimating the causal effect of elite messages on public support for European integration employing instrumental variable estimation. The paper presents three main empirical results. First, we find that more negative elite messages about European integration do indeed decrease public support for Europe. Our analysis suggests that OLS estimates that ignore the endogeneity, omitted variables, and measurement problems that typically occur in estimating the effects of elite communication are biased, underestimating the magnitude of the effect of elite messages by fifty percent. Second, we find no evidence that this effect of elite messages varies for more politically aware individuals. Third, our estimates are inconsistent with a mainstreaming effect in which political awareness increases support for Europe in those political settings in which elites have a favorable consensus on the benefits of integration. This result is in sharp contrast to the OLS analysis that incorrectly suggests a mainstreaming effect.