摘要：We investigate whether previous evidence of the weakness of Tobin's q ratio to explain variation in capital expenditure investment stems from ignoring R&D as an alternative investment. Suppose q theory is true in the general sense that a firm’s incentive to invest increases with its relative market value. However, due to variations in industry technology, individual firms vary in their propensities to make physical vs. intellectual property (IP) investment. The conventionally calculated q failed to make distinction of the propensities for the two investments types, q did a poor job in explaining the firm level investment. We develop a modified q model that account for individual firms' ex ante propensities to make these alternative types of investment. Using data on U.S. firms for 1974-2008, we test the model’s power to explain firm’s investment. The evidence shows strong support for modified model. Q ratio accounting for investment propensities explains more than 27.2% (61%) of capital expenditure (R&D) investment variations compared to about 0.9% (10.6%) obtained via conventional regression. Our approach yields strong and robust support for q theory. To our knowledge, our study is the first to propose a modified q measure to account investment propensity in the empirical corporate investment literature. We also document evidence of the influence of financial constraints on investment.
