چرخه های رشد موجودی با سرمایه گذاری تحت پوشش بدهی Inventory growth cycles with debt-financed investment

1. Introduction Inventory fluctuations have been known for a long time to be a major component of the business cycle (Abramovitz, 1950). According to Blinder (1981), even though investment in inventory accounts for a very small fraction of output (about 1 percent in the U.S.), changes in inventory investment account for a disproportionately large fraction of changes in output over the cycle (about 60 percent on average for seven postwar recessions in the U.S.). Nevertheless, inventory dynamics has received relatively little attention in the theoretical literature. A review of earlier models is provided in Blinder and Maccini (1991), where it is observed that, whereas “the prevailing micro theory viewed inventories as a stabilizing factor”, the data shows that output is more volatile than final sales (namely outputless inventory investment), suggesting a destabilizing role for inventories in macroeconomics. The landscape has not changed significantly since then, with a few recent papers focussed onincorporating inventories infullymicro foundedgeneral equilibrium models (Wang et al., 2014; Wen, 2011). As remarked in these papers, explaining inventories in a frictionless general equilibrium model is as challenging as explaining money, forcing this type of ∗ Corresponding author. E-mail address: grasselli@math.mcmaster.ca (M.R. Grasselli). analysis to rely on frictions, such as delivery costs and stockoutavoidance motives, akin to the attempts to incorporate a financial sector into DSGE models. In this paper, we follow an alternative approach based on disequilibrium models where sluggish adjustment, adaptive expectations, and sectoral averages replace market clearing, rational expectations, and representative agents (Godley and Lavoie, 2007). Our starting point is the growth cycles model proposed in Franke (1996) along the lines originally formulated in Metzler (1941): investment in inventory adjusts to a desired inventoryto-expected-sales ratio, whereas expected sales themselves adapt taking into account fluctuating demand.As shown in Franke (1996), the interplay between the long-run growth trend and short-run adjustment of inventory stock and expected sales determine the stability of the model. Whereas sufficiently sluggish adjustments promote stability, the model exhibits dynamic instability if the adjustment speeds exceed certain thresholds. Moreover, a flexible inventory adjustment speed can lead to persistent cyclical behaviour. The model in Franke (1996) is described by means of a two-dimensional dynamical system with normalized expected sales and inventory levels (or equivalently, capacity utilization) as state variables and therefore necessarily neglects several other macroeconomic dynamic feedback channels.