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We propose a simple and intuitive method for estimating betas when factors are measured with error: ordinary least squares instrumental variable estimator (OLIVE). OLIVE performs well when the number of instruments becomes large, while the performance of conventional instrumental variable methods becomes poor or even infeasible. In an empirical application, OLIVE beta estimates improve R-squared significantly. More importantly, our results help resolve two puzzling findings in the prior literature: first, the sign of average risk premium on the beta for market return changes from negative to positive; second, the estimated value of average zero-beta rate is no longer too high.JEL Classifications: C30, G12.1

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We find that opinion divergence among professional investment managers is commonplace, using a large sample of transaction-level institutional trading data. When managers trade together, future returns are similar regardless if they are all buying or selling, inconsistent with the notion that professional investment managers possess stock picking ability or private information that is of investment value. However, when managers trade against each other, subsequent returns are low, especially for stocks that are difficult to short. This U-shaped disagreement-return relationship is consistent with Miller's (1977) hypothesis that, in the presence of short-sale constraints, opinion divergence can cause an upward bias in prices. Copyright (c) 2008 The Authors Journal compilation (c) 2008 Blackwell Publishing Ltd.