In the late 1930s, Macaulay [7] and Hicks [6] independently introduced the concept of duration as a measure of the length of a stream of cash flows and a measure of the elasticity of the present value of the stream with respect to a change in the rate of discount, respectively. Approximately 15 years later, Reddington [8] and Heynes and Kirton [5] used the concept to develop interest rate immunization rules for the portfolio management of insurance companies. More recently, Fisher and Weil [1] have developed duration based rules to help investors find investments that will insure them of having some fixed amount of money available at a specific future point in time. In [2], Grove uses duration to link the investor's decision to speculate or immunize with his subjective forecast of future interest rate movements. Finally, Haugen and Wichern [3, 4] show the relationship between duration and the characteristics of bonds and stocks. Also, in analyzing the effect of financial leverage on interest rate risk, they demonstrate how the financial manager can manipulate the capital structure of his firm, so as to render the present value of the common stock insensitive to changes in the rate of interest.

In a world characterized by perfect and complete capital markets, the success (or failure) of a merger is judged by the merger's impact on stockholder wealth. With completeness, the merger's impact on the probability distribution generating stockholder returns is unimportant. The perfect market assumption guarantees that the stockholder not satisfied with the consolidated firm's return distribution can frictionlessly sell his shares and reorder his portfolio; hence his only concern is the merger's impact on wealth. However, if we acknowledge the existence of commissions, taxes, and other frictions, or if markets are not complete, the merger's impact on the stockholder return distribution becomes relevant. In this study we will analyze 149 mergers involving large N.Y.S.E. firms. We will examine four different hypotheses related to the impact of merger on attributes of the stockholder return distribution. We focus our analysis on risk-related attributes including beta, total variance, residual variance, and several other risk-related attributes. In a companion paper, merger's impact on wealth is calculated for the same sample but will not be reported here.