Private Information, Short Sales, and Long-Run Performance

The relationship of information flow and market price formation are central to the basic tenets of financial economics. Whereas information is usually treated as being either public or private(monopolistic), most empirical studies focus on the price effects of public announcements. More recent research has centered more on the role of private information, such as insider trading, in efficient pricing and whether such trading increases investor welfare. Typically, 'insider trading' refers to an officer that trades in his/her company's shares. Insider trading, however, also refers to anyone who generates private, albeit costly, information concerning a stock's fundamental value. Normally, such insider activity is more difficult to ascertain. One way in which negative information is revealed is through short-selling activity, especially the monthly short-interest positions reported by the national stock exchanges. Diamond and Verrecchia(1987) provide a theoretical paradigm that predicts a negative price adjustment upon announcement of n company's monthly short interest, if the short interest displays an unusual increase and is correlated with negative information that is not yet public. Empirical studies of the short-run, negative price effect predicted by Diamond and Verrecchia find mixed results. One explanation is that the time period studied is too short for the market to absorb the informational content of these announcements. One reason is that these announcements are an ambiguous signal that requires more individuals and time to collect and act on the same information before full revelation occurs or before the implicit information becomes publicly known. This 'long delayed reaction' also serves as a motivation for related research on the wealth effect of mergers, share repurchases, and initial equity offerings in which long-run performance differs from the initial, short-run reaction to such announcements or offerings.