Empirical Methods in Corporate Finance

This paper identities five common risk factors in the returns on stocks and bonds. There are three stock-market factors: an overall market factor and factors related to firm size and book-to-market equity. There are two bond-market factors. related to maturity and default risks. Stock returns have shared variation due to the stock-market factors, and they are linked to bond returns through shared variation in the bond-market factors. Except for low-grade corporates. the bond-market factors capture the common variation in bond returns. Most important. the five factors seem to explain average returns on stocks and bonds.

We analyze tests for long-run abnormal returns and document that two approaches yield well-specified test statistics in random samples. The first uses a traditional event study framework and buy-and-hold abnormal returns calculated using carefully constructed reference portfolios. Inference is based on either a skewnessadjusted t-statistic or the empirically generated distribution of long-run abnormal returns. The second approach is based on calculation of mean monthly abnormal returns using calendar-time portfolios and a time-series t-statistic. Though both approaches perform well in random samples, misspecification in nonrandom samples is pervasive. Thus, analysis of long-run abnormal returns is treacherous.

Defenders of market efficiency argue that anomalies involving long-term abnormal returns are not robust to alternative methodologies. We argue that because various methodologies use different weighting schemes, the magnitude of abnormal returns should differ, and in a predictable manner. Three problems are identified that cause low power in value-weighted three-factor time series regressions when abnormal returns following managerial actions are being estimated. We illustrate the sensitivities in the context of the new issues puzzle as well as with simulations. More generally, multifactor models as currently used do not, and cannot, test market efficiency.

原文链接：

https://pdfs.semanticscholar.org/c718/44896fa8b03584669daf5ebf1e0385e4748a.pdf