Robust Monetary Policy Rules with Unknown Natural Rates

Abstract

natural rate is an abstraction; like faith, it is seen by its works. can only say if bank policy succeeds in stabilizing prices, bank rate must have been brought in line with natural rate, but if it does not, it must not have been. (1) THE CONVENTIONAL PARADIGM for conduct of monetary policy calls for monetary authority to attain its objectives of a low and stable rate of inflation and full employment by adjusting its short-term interest rate instrument--in United States, federal funds rate--in response to economic developments. In principle, when aggregate demand and employment fall short of economy's natural levels of output and employment, or when other deflationary concerns appear on horizon, central bank should ease monetary policy by bringing real interest rates below economy's natural rate of interest for some Conversely, central bank should respond to inflationary concerns by adjusting interest rates upward so as to bring real interest rates above natural rate. In this setting, natural rate of unemployment is unemployment rate consistent with stable inflation; natural rate of interest is real interest rate consistent with unemployment being at its natural rate, and therefore with stable inflation. (2) In carrying out this strategy in practice, policymaker would ideally have accurate, quantitative, contemporaneous readings of natural rate of interest and natural rate of unemployment. Under those circumstances, economic stabilization policy would be relatively straightforward. However, an important difficulty complicates policymaking in practice and may limit scope for stabilization policy is policymakers do not know values of these natural rates in real time, is, when they make policy decisions. Indeed, even in hindsight there is considerable uncertainty regarding natural rates of unemployment and interest, and ambiguity about how best to model and estimate natural rates. Milton Friedman, arguing against natural rate-based policies in his presidential address to American Economic Association, posited One problem is [the policymaker] cannot know what `natural' rate is. Unfortunately, we have as yet devised no method to estimate accurately and readily natural rate of either interest or unemployment. And `natural' rate will itself change from time to time. (3) Friedman's comments echo those made decades earlier by John H. Williams and by Gustav Cassel, who wrote of natural rate of interest: The bank cannot know at a certain moment what is equilibrium rate of interest of capital market. (4) Even earlier, Knut Wicksell stressed the natural rate is not fixed or unalterable in magnitude. (5) Recent research using modern statistical techniques to estimate natural rates of unemployment, output, and interest indicates this problem is no less relevant today than it was 35, 75, or 105 years ago. These measurement problems appear particularly acute in presence of structural change, when natural rates may vary unpredictably, subjecting estimates to increased uncertainty. Douglas Staiger, James Stock, and Mark Watson document estimates of a time-varying natural rate of unemployment are very imprecise. (6) Orphanides and Simon van Norden show estimates of related concept of natural rate of output (that is, potential output) are likewise plagued by imprecision. (7) Similarly, Thomas Laubach and John C. Williams document great degree of uncertainty regarding estimates of natural rate of interest. (8) These difficulties have led some observers to discount usefulness of natural rate estimates for policymaking. William Brainard and George Perry conclude that conventional estimates from a NAIRU [nonaccelerating-inflation rate of unemployment] model do not identify full employment range with a degree of accuracy is useful to policymaking. …