An Evaluation of Shareholder Activism

We develop a method to evaluate shareholder activism when an activist targets firms whose shareholders are diversified portfolio holders of possibly correlated firms. Our method of evaluation takes the portfolios of all of the shareholders, including the activist, as its basis of analysis. We model the activist from the time of the acquisition of a foothold in the target firm through the moment when the activist divests the newly acquired shares. We assume that during this period, all exchanges of securities, and their corresponding prices, are achieved in Walrasian markets in which all participants, including the activist, are risk-averse price-takers. Using the derived series of price changes of all the firms in the market, as well as the derived series of changes in all the portfolio holdings over this period, we evaluate the impact of activism on the activist, on the group of other shareholders, and on the combined group. We show that when activism is beneficial to the activist, the group of other investors may not benefit; furthermore, even when the activist benefits from activism, the value of the market may decrease. When the activist benefits from activism, an increase in the value of the market is a necessary but not sufficient condition for the group of other investors to benefit also from activism. In addition, we show that the combined group, the activist plus the group of other investors, benefits if and only if the value of the market increases and, under this condition, either the activist or the group of other investors, but not necessarily both, benefits