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Discussion Paper

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A firm may acquire additional capital input by purchasing new capital or by increasing the utilization of its current capital. The margin between capita accumulation and capital utilization is studied in a model of dynamic factor demand where the firm chooses capital, labor, and their rates of utilization. A direct measure of capital utilization — the work week of capital — is incorporated into the theory and estimates. The methodology advocated by Hansen and Singleton (1982) is used to obtain estimates of the model’s parameters. This methodology allows the firm’s decision problem to depend on expected values of future endogenous and exogenous functional form or the distribution of shocks to the system. The estimates imply that capital stock is costly to adjust while the work week of capital is essentially costless to adjust. Hence, the work week of capital overshoots the steady state when innovations in policy or other shocks change the demand for capital. Short run variation in the demand for capital is met by changing utilization. Long run variation is met by changing the stock. The estimated response of the capital stock to changes in its price and in the required rate of return is substantial and it takes place more quickly than found in other estimates. These results provide an important challenge to the view that input prices and required rates of return are empirically unimportant in models of the demand for capital.

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