Competition and Bias
54 Pages Posted: 17 Mar 2008
Date Written: March 2008
We attempt to measure the effect of competition on bias in the context of analyst earnings forecasts, which are known to be excessively optimistic due to conflicts of interest. Our instrument for competition is mergers of brokerage houses, which result in the firing of analysts because of redundancy (e.g., one of the two oil analysts is let go) and other reasons such as culture clash. We use this decrease in analyst coverage for stocks covered by both merging houses before the merger (the treatment sample) to measure the causal effect of competition on bias. We find the treatment sample simultaneously experiences a decrease in analyst coverage and an increase in optimism bias the year after the merger relative to a control group of stocks, consistent with competition reducing bias. The implied economic effect from our natural experiment is significantly larger than estimates from OLS regressions that do not correct for the endogeneity of coverage. And this effect is much more significant for stocks with little initial analyst coverage or competition.
Keywords: analyst bias, competition
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