In the 1988-2004 micro data collected by the U.S. Bureau of Labor Statistics for the CPI, price changes are frequent (every 4-7 months, depending on the treatment of sale prices) and large in absolute value (on the order of 10%). The size and timing of price changes varies considerably for a given item, but the size and probability of a price change are unrelated to the time since the last price change. Movements in aggregate inflation reflect movements in the size of price changes rather than the fraction of items changing price, due to offsetting movements in the fraction of price increases and decreases. Neither leading time-dependent models (Taylor or Calvo) nor 1 st generation state-dependent models match all of these facts. Some 2 nd generation state-dependent models, however, appear broadly consistent with the empirical patterns.

In the 1988-2004 micro data collected by the U.S. Bureau of Labor Statistics for the CPI, price changes are frequent (every 4-7 months, depending on the treatment of sale prices) and large in absolute value (on the order of 10%). The size and timing of price changes varies considerably for a given item, but the size and probability of a price change are unrelated to the time since the last price change. Movements in aggregate inflation reflect movements in the size of price changes rather than the fraction of items changing price, due to offsetting movements in the fraction of price increases and decreases. Neither leading time-dependent models (Taylor or Calvo) nor 1 st generation state-dependent models match all of these facts. Some 2 nd generation state-dependent models, however, appear broadly consistent with the empirical patterns.

Real rigidities that limit the responsiveness of real marginal cost to output are a key ingredient of sticky price models necessary to account for the dynamics of output and inflation. We argue here, in the spirit of Bils and Kahn (2000), that the behavior of marginal cost over the cycle is directly related to that of inventories, data on which is readily available. We study a menu cost economy in which firms hold inventories in order to avoid stockouts and to economize on fixed ordering costs.We find that, for low rates of depreciation similar to those in the data, inventories are highly sensitive to changes in the cost of holding and acquiring them over the cycle. This implies that the model requires an elasticity of real marginal cost to output approximately equal to the inverse of the elasticity of intertemporal substitution in order to account for the countercyclical inventory-tosales ratio in the data. Stronger real rigidities lower the cost of acquiring and holding inventories during booms and counterfactually predict a procyclical inventory-to-sales ratio. JEL classification: E31, F12 Bank classification: Business fluctuations and cycles; Transmission of monetary policy RésuméLes rigidités réelles qui limitent la sensibilité du coût marginal réel aux fluctuations de la production sont un élément essentiel des modèles à prix rigides, nécessaire pour rendre compte de

Bank of Canada staff working papers provide a forum for staff to publish work-in-progress research independently from the Bank's Governing Council. This research may support or challenge prevailing policy orthodoxy. Therefore, the views expressed in this paper are solely those of the authors and may differ from official Bank of Canada views. No responsibility for them should be attributed to the Bank.

Bank of Canada staff working papers provide a forum for staff to publish work-in-progress research independently from the Bank's Governing Council. This research may support or challenge prevailing policy orthodoxy. Therefore, the views expressed in this paper are solely those of the authors and may differ from official Bank of Canada views. No responsibility for them should be attributed to the Bank.