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An Empirical Model of Inventory Investment by Durable Commodity Intermediaries

This paper introduces a new detailed data set of high-frequency observations on inventory investment by a U.S. steel wholesaler. Our analysis of these data leads to six main conclusions: orders and sales are made infrequently; orders are more volatile than sales; order sizes vary considerably; there is substantial high-frequency variation in the firm's sales prices; inventory/sales ratios are unstable; and there are occasional stockouts. We model the firm generically as a durable commodity intermediary that engages in commodity price speculation. We demonstrate that the firm's inventory investment behavior at the product level is well approximated by an optimal trading strategy from the solution to a nonlinear dynamic programming problem with two continuous state variables and one continuous control variable that is subject to frequently binding inequality constraints. We show that the optimal trading strategy is a generalized (S,s) rule. That is, whenever the firm's inventory level q falls below the order threshold s(p) the firm places an order of size S(p) - q in order to attain a target inventory level S(p) satisfying S(p) >= s(p), where p is the current spot price at which the firm can purchase unlimited amounts of the commodity after incurring a fixed order cost K. We show that the (S,s) bands are decreasing functions of p, capturing the basic intuition of commodity price speculation, namely, that it is optimal for the firm to hold higher inventories when the spot price is low than when it is high in order to profit from "buying low and selling high." We simulate a calibrated version of this model and show that the simulated data exhibit the key features of inventory investment we observe in the data.

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File URL: http://cowles.econ.yale.edu/P/cd/d12a/d1228.pdf
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Paper provided by Cowles Foundation for Research in Economics, Yale University in its series Cowles Foundation Discussion Papers with number 1228.

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Length: 45 pages
Date of creation: Jun 1999
Date of revision:
Publication status: Published in Carnegie-Rochester Conference Series on Public Policy, June 2000
Handle: RePEc:cwl:cwldpp:1228
Contact details of provider: Postal: Yale University, Box 208281, New Haven, CT 06520-8281 USA
Phone: (203) 432-3702
Fax: (203) 432-6167
Web page: http://cowles.econ.yale.edu/

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Order Information: Postal: Cowles Foundation, Yale University, Box 208281, New Haven, CT 06520-8281 USA

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  1. Jonas D.M. Fisher & Andreas Hornstein, 1996. "(S, s) inventory policies in general equilibrium," Working Paper Series, Macroeconomic Issues WP-96-24, Federal Reserve Bank of Chicago.
  2. Martin S. Eichenbaum, 1988. "Some Empirical Evidence on the Production Level and Production Cost Smoothing Models of Inventory Investment," NBER Working Papers 2523, National Bureau of Economic Research, Inc.
  3. West, Kenneth D, 1986. "A Variance Bounds Test of the Linear Quadratic Inventory Model," Journal of Political Economy, University of Chicago Press, vol. 94(2), pages 374-401, April.
  4. Martin Feldstein & Alan Auerbach, 1976. "Inventory Behavior in Durable-Goods Manufacturing: The Target-Adjustment Model," Brookings Papers on Economic Activity, Economic Studies Program, The Brookings Institution, vol. 7(2), pages 351-408.
  5. Blinder, Alan S, 1986. "More on the Speed of Adjustment in Inventory Models," Journal of Money, Credit and Banking, Blackwell Publishing, vol. 18(3), pages 355-65, August.
  6. Miron, Jeffrey A & Zeldes, Stephen P, 1988. "Seasonality, Cost Shocks, and the Production Smoothing Models of Inventories," Econometrica, Econometric Society, vol. 56(4), pages 877-908, July.
  7. Blanchard, Olivier J, 1983. "The Production and Inventory Behavior of the American Automobile Industry," Journal of Political Economy, University of Chicago Press, vol. 91(3), pages 365-400, June.
  8. Valerie A. Ramey & Kenneth D. West, 1997. "Inventories," NBER Working Papers 6315, National Bureau of Economic Research, Inc.
    • Ramey, Valerie A. & West, Kenneth D., 1999. "Inventories," Handbook of Macroeconomics, in: J. B. Taylor & M. Woodford (ed.), Handbook of Macroeconomics, edition 1, volume 1, chapter 13, pages 863-923 Elsevier.
  9. John Rust & Joseph Traub & Henryk Wozniakowski, 1999. "No Curse of Dimensionality for Contraction Fixed Points Even in the Worst Case," Computational Economics 9902001, EconWPA.
  10. James A. Kahn & Mark Bils, 2000. "What Inventory Behavior Tells Us about Business Cycles," American Economic Review, American Economic Association, vol. 90(3), pages 458-481, June.
  11. Angus Deaton & Guy Laroque, 1990. "On The Behavior of Commodity Prices," NBER Working Papers 3439, National Bureau of Economic Research, Inc.
  12. Eichenbaum, Martin S., 1984. "Rational expectations and the smoothing properties of inventories of finished goods," Journal of Monetary Economics, Elsevier, vol. 14(1), pages 71-96, July.
  13. Andrew B. Abel, 1985. "Inventories, Stock-Outs, and Production Smoothing," NBER Working Papers 1563, National Bureau of Economic Research, Inc.
  14. John Rust, 1997. "Using Randomization to Break the Curse of Dimensionality," Econometrica, Econometric Society, vol. 65(3), pages 487-516, May.
  15. Kahn, James A, 1992. "Why Is Production More Volatile Than Sales? Theory and Evidence on the Stockout-Avoidance Motive for Inventory-Holding," The Quarterly Journal of Economics, MIT Press, vol. 107(2), pages 481-510, May.
  16. Jeffrey A. Miron & Stephen P. Zeldes, 1988. "Production, Sales, and the Change in Inventories: An Identity That Doesn`t Add Up," NBER Working Papers 2765, National Bureau of Economic Research, Inc.
  17. Hall, George J., 2000. "Non-convex costs and capital utilization: A study of production scheduling at automobile assembly plants," Journal of Monetary Economics, Elsevier, vol. 45(3), pages 681-716, June.
  18. Kahn, James A, 1987. "Inventories and the Volatility of Production," American Economic Review, American Economic Association, vol. 77(4), pages 667-79, September.
  19. Timothy F. Bresnahan & Valerie A. Ramey, 1992. "Output Fluctuations at the Plant Level," NBER Working Papers 4105, National Bureau of Economic Research, Inc.
  20. Caplin, Andrew S, 1985. "The Variability of Aggregate Demand with (S, s) Inventory Policies," Econometrica, Econometric Society, vol. 53(6), pages 1395-1409, November.
  21. Ramey, Valerie A, 1991. "Nonconvex Costs and the Behavior of Inventories," Journal of Political Economy, University of Chicago Press, vol. 99(2), pages 306-34, April.
  22. repec:cup:cbooks:9780521326162 is not listed on IDEAS
  23. Fair, Ray C., 1989. "The production-smoothing model is alive and well," Journal of Monetary Economics, Elsevier, vol. 24(3), pages 353-370, November.
  24. Blinder, Alan S, 1986. "Can the Production Smoothing Model of Inventory Behavior Be Saved?," The Quarterly Journal of Economics, MIT Press, vol. 101(3), pages 431-53, August.
  25. John Rust, 1997. "A Comparison of Policy Iteration Methods for Solving Continuous-State, Infinite-Horizon Markovian Decision Problems Using Random, Quasi-random, and Deterministic Discretizations," Computational Economics 9704001, EconWPA.
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