Market Structure and Financial Leverage: Does Market Power Affect Debt and Equity Decisions?
The issue of capital structure has been a subject of intense debate among researchers for the last quarter of a century. Various theories have been developed to explain the way a firm chooses its capital structure. These theories make predictions that range from the Modigliani-Miller  assertion that, in the absence of corporate taxes, capital structure has no effect on the value of a firm, to the proposition that, in the presence of taxes, the optimal capital structure is 100% debt (Modigliani and Miller ). But neither of the theories explains the "real world" behavior of firms. It has been observed that firms choose a capital structure that lies somewhere between the two extremes mentioned above. This has led to the belief that there may exist such a thing as an "optimal" capital structure that includes both debt and equity.
A large body of empirical research provides evidence that supports the view that firms do choose a capital structure that includes debt and equity and that there is a significant amount of commonality in capital structures (regarding the choice of financial leverage) of firms operating in the same industry. This finding implies that while different industries may exhibit widely differing capital structures, firms in the same industry choose capital structures that are similar. In an earlier study by Scott , inter-industry differences in financial leverage were shown to be far more significant than intra-industry differences.
Researchers have used a number of factors - both firm specific and industry-wide - to explain a firm's choice of a particular level of financial leverage. DeAngelo and Masulis  presented a hypothesis regarding the relationship between a firm's non-debt tax-shields and its capital structure. Boquist and Moore  investigated this relationship at the firm level and concluded that such relationship between these two variables is exactly opposite of the one hypothesized by DeAngelo and Masulis.
A more recent study by Bradley, Jarrel, and Kim  provided empirical evidence that, in addition to the firm's non-debt tax-shields, its expenditure on advertising and R&D will influence the firm's choice of financial leverage. Their findings also confirmed the results of the Chaplinsky  investigation that showed a link between the variability of firm value and its choice of leverage. It should be noted, however, that the Bradley, Jarrel, and Kim study  was based on firms classified according to the two-digit SIC code. In contrast, the analysis we present in this paper is based on firms grouped according to the four-digit SIC code.
MARKET STRUCTURE AND CAPITAL
STRUCTURE: THE HYPOTHESIS
Weston and Copeland , among others, mention sales stability and variability in earnings as two major influences affecting a firm's choice of capital structure. The conclusions of microeconomic theory strongly suggest that firms in highly concentrated industries, where significant entry barriers exist, enjoy more stable sales and earnings than do firms in less concentrated industries, where lower entry barriers are dominant. This suggests that a firm's market power in its industry may have a significant effect on the firm's choice of financial leverage. The purpose of this study is to test the hypothesis that the choice of financial leverage by a firm is influenced by the market structure of its industry.
Empirical research on this issue has produced contradictory results. Sullivan  and Hurdle  each found an inverse relationship between the level of concentration and a leverage ratio, debt to total invested capital. Melicher, Rush, and Winn , however, were unable to find any relationship between financial structure and levels of industry concentration. Sullivan  and Melicher, Rush, and Winn  …