ترازنامه بانک مرکزی به عنوان ابزار سیاست پولی

We extend a standard New Keynesian model to allow an analysis of “unconventional” dimensions of policy alongside traditional interest-rate policy. We find that quantitative easing in the strict sense is likely to be ineffective, but that targeted asset purchases by a central bank can instead be effective when financial markets are sufficiently disrupted, and we discuss the conditions under which such interventions increase welfare. We also discuss optimal policy with regard to the payment of interest on reserves.

The recent global financial crisis has confronted central banks with a number of questions beyond the scope of standard accounts of the theory of monetary policy. Monetary policy is ordinarily considered solely in terms of the choice of an operating target for a short-term nominal interest rate, such as the federal funds rate in the case of the Federal Reserve. Yet during the recent crisis, other dimensions of policy have occupied much of the attention of central bankers. One is the question of the appropriate size of the central bank's balance sheet. In fact, the Fed's balance sheet has grown dramatically in size since the fall of 2008 (Fig. 1 and Fig. 2). Fig. 1. Liabilities of the Federal Reserve. (Source: Federal Reserve Board.) Figure options Fig. 2. Assets of the Federal Reserve. (Source: Federal Reserve Board.) Figure options As shown in Fig. 1, the component of the Fed's liabilities constituted by reserves held by depository institutions has changed in an especially remarkable way: by the fall of 2008 reserves were more than 100 times larger than they had been only a few months earlier. This explosive growth has led some commentators to suggest that the main instrument of US monetary policy has changed, from an interest-rate policy to one often described as “quantitative easing.” Does it make sense to regard the supply of bank reserves (or perhaps the monetary base) as an alternative or superior operating target for monetary policy? Does this (as some would argue) become the only important monetary policy decision once the overnight rate (the federal funds rate) has reached the zero lower bound, as it effectively has in the US since December 2008? And now that the Federal Reserve has legal authorization to pay interest on reserves (under the Emergency Economic Stabilization Act of 2008), how should this additional potential dimension of policy beused? The past two years have also seen dramatic developments with regard to the composition of the asset side of the Fed's balance sheet (Fig. 2). Whereas the Fed had largely held Treasury securities on its balance sheet prior to the fall of 2007, other kinds of assets — a variety of new “liquidity facilities” , new programs under which the Fed essentially became a direct lender to certain sectors of the economy, and finally targeted purchases of certain kinds of assets, including more than a trillion dollars’ worth of mortgage-backed securities — have rapidly grown in importance, and decisions about the management of these programs have occupied much of the attention of policymakers during the recent period. How should one think about the aims of these programs, and the relation of this new component of Fed policy to traditional interest-rate policy? Is Federal Reserve credit policy a substitute for interest-rate policy, or should it be directed to different goals than those toward which interest-rate policy is directed? These are clearly questions that a theory of monetary policy adequate to our present circumstances must address. Yet not only have they been the focus of relatively little attention until recently, but the very models commonly used to evaluate the effects of alternative prescriptions for monetary policy have little to say about them. Many models used for monetary policy analysis — both theoretical models used in normative discussions of ideal monetary policy commitments, and quantitative models used for numerical simulation of alternative policies — abstract altogether from the central bank's balance sheet, simply treating a short-term nominal interest rate as if it were under the direct control of the monetary authorities, and analyzing how that interest rate should be adjusted.2 But such a framework rules out the kinds of questions that have recently preoccupied central bankers from thestart. In this paper, we extend a basic New Keynesian model of the monetary transmission mechanism to explicitly include the central bank's balance sheet as part of the model. In addition to making more explicit the ways in which a central bank is able to (indirectly) exert control over the policy rate, the extended model allows us to address questions about other dimensions of policy of the sort just posed. In order to make these questions non-trivial, we also introduce non-trivial heterogeneity in spending opportunities, rather than adopting the familiar device of the “representative household,” so that financial intermediation matters for the allocation of resources; we introduce imperfections in private financial intermediation, and the possibility of disruptions to the efficiency of intermediation, for reasons taken here as exogenous, so that we can examine how such disturbances affect the desirability of central-bank credit policy; and we allow central-bank liabilities to supply transactions services, so that they are not assumed to be perfect substitutes for privately issued financial instruments of similar maturity and with similar state-contingent payoffs. Finally, we consider the conduct of policy both when the zero lower bound on the policy rate is not a binding constraint, and also whenit is. Section 2 outlines the structure of our model, with primary attention to the way that we model financial intermediation and the policy choices available to the central bank. Section 3 then uses the model to discuss changes in the supply of bank reserves as a dimension of policy, and the related question of the rate of interest that should be paid on reserves. Section 4 then turns to the question of the optimal composition of the central bank's asset portfolio, and Section 5 concludes.