Market Valuation and the q Theory of Investment

This study re-evaluates the role of the stock market in Japanese corporate investment decisions based on time-series data. Employing the time-series technique, we examine why the performance of Tobin's average q -type investment function is poor. We construct a series of average q and another of marginal q (a more fundamental profitability measure of investment) and investigate the relationship between the two. A cointegrating relationship is not detected between the two measures, both of which have a unit root. The divergence of average q from marginal q is not narrowed even if the imperfect competition of the output market is taken into consideration. We also examine which q measure is more relevant to Japanese corporate investment decisions by estimating separately the investment function with two measures of q as an explanatory variable. The estimation results show that entrepreneurs place more emphasis on marginal q than on average q in investment decisions.
JEL Classification Number: E22.     

Why Are Concavity Conditions Not Satisfied in the Cost Function? The Case of Japanese Manufacturing Firms during the Bubble Period*

This paper examines empirically the reasons why Japanese manufacturing firms frequently fail to satisfy concavity of the cost function in input prices. We focus on the ‘bubble period’ in the 1980s when land was in great demand and land prices soared. By estimating the translog cost function with land as one of production inputs, we find that violation of concavity mainly resulted from weak bank–firm relationship and massive transactions of land. We also demonstrate that elasticities of substitution between land and other inputs are estimated quite differently if the firms violating concavity are not excluded from the analysis.