Send correspondence to Mitchell A. Petersen, Kellogg School of Management, Northwestern University, and NBER, 2001 Sheridan Road, Evanston, IL 60208; telephone: 847-467-1281; email: firstname.lastname@example.org.
In corporate finance and asset pricing empirical work, researchers are often confronted with panel data. In these data sets, the residuals may be correlated across firms or across time, and OLS standard errors can be biased. Historically, researchers in the two literatures have used different solutions to this problem. This paper examines the different methods used in the literature and explains when the different methods yield the same (and correct) standard errors and when they diverge. The intent is to provide intuition as to why the different approaches sometimes give different answers and give researchers guidance for their use.