Weak instruments can produce biased IV estimators and hypothesis tests with large size distortions. But what, precisely, are weak instruments, and how does one detect them in practice? This paper proposes quantitative definitions of weak instruments based on the maximum IV estimator bias, or the...

This paper develops asymptotic distribution theory for generalized method of moments (GMM) estimators and test statistics when some of the parameters are well identified, but others are poorly identified because of weak instruments. The asymptotic theory entails applying empirical process theory...

Weak instruments arise when the instruments in linear instrumental variables (IV) regression are weakly correlated with the included endogenous variables. In generalized method of moments (GMM), more generally, weak instruments correspond to weak identification of some or all of the unknown...

The effect of school inputs on labor market outcomes is an important and controversial topic, both in the United States and in developing countries. A large literature about American schools has not settled debate on the issue. Card and Krueger (1992) estimate the effect of pupil/teacher ratios...

Movements in the value of corporate assets are justified by changes in expected future cash flow. The appropriate measure of cash flow for valuing assets is net payout, which is the sum of dividends, interest, and net repurchases of equity and debt. When discount rates are low and equity...

Conventional tests of the predictability of stock returns could be invalid, that is reject the null too frequently, when the predictor variable is persistent and its innovations are highly correlated with returns. We develop a pretest to determine whether the conventional t-test leads to invalid...