Julia K. Thomas

Inventories and the Business Cycle: An Equilibrium Analysis of (S,S) Policies

We develop an equilibrium business cycle model where nonconvex delivery costs lead producers of final goods to follow generalized (S,s) inventory policies with respect to intermediate goods. When calibrated to match the average inventory-to-sales ratio in postwar U.S. data, our model reproduces two-thirds of the cyclical variability of inventory investment. Moreover, inventory accumulation is strongly procyclical, and production is more volatile than sales, as in the data. The comovement between inventory investment and final sales is often interpreted as evidence that inventories amplify aggregate fluctuations. Our model contradicts this view. Despite the positive correlation between sales and inventory investment, we find that inventory accumulation has minimal consequence for the cyclical variability of GDP. In equilibrium, procyclical inventory investment diverts resources from the production of final goods; thus, it dampens cyclical changes in final sales, leaving GDP volatility essentially unaltered. Moreover, although business cycles arise solely from shocks to productivity and markets are perfectly competitive in our model, it nonetheless yields a countercyclical inventory-to-sales ratio.

Partial Adjustment Without Apology

Many kinds of economic behavior appear to be governed by discrete and occasional individual choices. Despite this, econometric partial adjustment models perform relatively well at the aggregate level. Analyzing the classic employment adjustment problem, we show how discrete and occasional microeconomic adjustment is well described by a new form of partial adjustment model that aggregates the actions of a large number of heterogeneous producers. We begin by describing a basic model of discrete and occasional adjustment at the micro level, where production units are essentially restricted to either operate with a fixed number of workers or shut down. We show that this simple model is observationally equivalent at the market level to the standard rational expectations partial adjustment model. We then construct a related, but more realistic, model that incorporates the idea that increases or decreases in the size of an establishments workforce are subject to fixed adjustment costs. In the market equilibrium of this model, employment responses to aggregate disturbances include changes both in employment selected by individual establishments and in the measure of establishments actively undertaking adjustment. Yet the model retains a partial adjustment flavor in its aggregate responses. Moreover, in contrast to existing models of discrete adjustment, our generalized partial adjustment model is sufficiently tractable to allow extension to general equilibrium.

Inflation and Interest Rates With Endogenous Market Segmentation

The authors examine a monetary economy where households incur fixed transactions costs when exchanging bonds and money and, as a result, carry money balances in excess of current spending to limit the frequency of such trades. As only a fraction of households choose to actively trade bonds and money at any given time, the market is endogenously segmented. Moreover, because households in this model economy have the ability to alter the timing of their trading activities, the extent of market segmentation varies over time in response to real and nominal shocks. The authors find that this added flexibility can substantially reinforce both sluggishness in aggregate price adjustment and the persistence of liquidity effects in real and nominal interest rates relative to that seen in models with exogenously segmented markets.

Modeling Inventories Over the Business Cycle

We search for useful models of aggregate fluctuations with inventories. We focus exclusively on dynamic stochastic general equilibrium models that endogenously give rise to inventory investment and evaluate two leading candidates: the (S,s) model and the stockout avoidance model. Each model is examined under both technology shocks and preference shocks, and its performance gauged by its ability to explain the observed magnitude of inventories in the U.S. economy, alongside other empirical regularities such as the procyclicality of inventory investment and its positive correlation with sales. We find that the (S,s) model is far more consistent with the behavior of aggregate inventories in the postwar U.S. when aggregate fluctuations arise from technology, rather than preference, shocks. The converse is true for the stockout avoidance model. Overall, while the (S,s) model performs well with respect to the inventory facts and other business cycle regularities, the stockout avoidance model does not. There, the essential motive for stocks is insufficient to generate inventory holdings near the data without destroying the models performance along other important margins. Finally, the stockout avoidance model appears incapable of sustaining inventories alongside capital. This suggests a fundamental problem in using reduced-form inventory models with stocks rationalized by this motive.