We propose a theory of asset pricing based on heterogeneous agents who continually adapt their expectations to the market that these expectations aggregatively create. And we explore the implications of this theory computationally using our Santa Fe artificial stock market. Asset markets, we argue, have a recursive nature in that agents ’ expectations are formed on the basis of their anticipations of other agents ’ expectations, which precludes expectations being formed by deductive means. Instead traders continually hypothesize—continually explore—expectational models, buy or sell on the basis of those that perform best, and confirm or discard these according to their performance. Thus individual beliefs or expectations become endogenous to the market, and constantly compete within an ecology of others ’ beliefs or expectations. The ecology of beliefs co-evolves over time. Computer experiments with this endogenous-expectations market explain one of the more striking puzzles in finance: that market traders often believe in such concepts as technical trading, “market psychology, ” and bandwagon effects, while academic theorists believe in market efficiency and a lack of speculative opportunities. Both views, we show, are correct, but within different regimes. Within a regime where investors explore alternative expectational models at a low rate, the market settles into the rational-

NBER. Tim Opler also holds an appointment at Deutsche Morgan Grenfell. We thank

This paper employs stochastic simulations of a small structural rational expectations model to investigate the consequences of the zero bound on nominal interest rates. We find that if the economy is subject to stochastic shocks similar in magnitude to those experienced in the U.S. over the 1980s and 1990s, the consequences of the zero bound are negligible for target inflation rates as low as 2 percent. However, the effects of the constraint are non-linear with respect to the inflation target and produce a quantitatively significant deterioration of the performance of the economy with targets between 0 and 1 percent. The variability of output increases significantly and that of inflation also rises somewhat. The stationary distribution of output is distorted with recessions becoming somewhat more frequent and longer lasting. Our model also uncovers that the asymmetry of the policy ineffectiveness induced by the zero bound generates a non-vertical long-run Phillips curve. Output falls increasingly short of potential with lower inflation targets. At zero average inflation, the output loss is in the order of 0.1 percentage points. We also investigate the consequences of the constraint on the analysis of optimal policy based on the inflation-output variability frontier. We demonstrate that in the presence of the zero bound, the variability frontier is distorted as the inflation target approaches zero. As a result comparisons of alternative policy rules that ignore the zero bound can be seriously misleading.

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We use the link between financial constraints and a firm’s demand for liquidity to develop a new test of the effect of financial constraints on firm policies. The effect of financial constraints can be captured by a firm’s propensity to save cash out of incremental cash inflows (the cash flow sensitivity of cash). While constrained firms should have a positive cash flow sensitivity of cash, unconstrained firms ’ cash savings should not be systematically related to cash flows. We estimate the cash flow sensitivity of cash using a large sample of manufacturing firms over the 1971-2000 period and find that firms that are more likely to be financially constrained display a significantly positive cash flow sensitivity of cash, while unconstrained firms do not. Also consistent with our argument, we find that constrained firms ’ cash flow sensitivity of cash increases during recessions, while unconstrained firms ’ cash—cash flow sensitivity is unaffected by macroeconomic innovations. The use of cash flow sensitivities of cash appears to be a theoretically justified, empirically useful method to test for the importance of financial constraints.

This paper adopts Keynes ' view that shocks to the marginal efficiency of investment are important for business fluctuations, but incorporates it in a neoclassical framework with endogenous capacity utilization. Increases in the efficiency of newly produced investment goods stimulate the formation of "new " capital and more intensive utilization and accelerated depreciation of "old " capital. Theoretical and quantitative analysis suggests that the shocks and transmission mechanism studied here may be important elements of business cycles. In the real-business cycle models of the type developed by Finn Kydland and Edward Prescott (1982), and John Long and Charles Plosser (1983), the cycles are generated by exogenous shocks to the production function. A stylized version of the main mechanism working in these models can be described as follows. Dynamic optimizing behavior on the part of agents in the economy implies that both consumption and investment react positively to these direct shocks to output. Since the marginal productivity of labor is directly affected, employment is also procyclical. The resulting capital accumulation provides a channel of persistence, even if the technology shocks are serially uncorrelated. Hence, these productivity shocks are able to generate, from a neoclassical framework, co-movements of macroeconomic variables and persistence of fluctuations that conform to those typically observed during business cycles. In contrast with the mechanism described above, where investment reacts to changes in output, the present paper adopts John Maynard Keynes ' (1936) view that it is shocks to the marginal efficiency of investment that are important for generating out-

Zeldes (1989), Carroll (1992; 1993), and others have shown that optimal consumption behavior for consumers facing income uncertainty can be remarkably di erent from the certainty-equivalent case. Carroll (1992; 1993) observes that many of the di erences can be attributed to the concavity of the consumption function under uncertainty, but he does not describe the conditions under which the consumption function will be concave. We show that if labor income is stochastic, the consumption function will be concave for many commonly used utility functions, and if both labor income and capital income are stochastic, the consumption function is concave for an even broader group of utility functions.

Can neoclassical theory account for the Great Depression in the United States--- both the downturn in output between 1929 and 1933 and the recovery between 1934 and 1939? Yes and no. Given the large real and monetary shocks to the U.S. economy during 1929--33, neoclassical theory does predict a long, deep downturn. However, theory predicts a much different recovery from this downturn than actually occurred. Given the period's sharp increases in total factor productivity and the money supply and the elimination of deflation and bank failures, theory predicts an extremely rapid recovery that returns output to trend around 1936. In sharp contrast, real output remained between 25 and 30 percent below trend through the late 1930s. We conclude that a new shock is needed to account for the Depression's weak recovery. A likely culprit is New Deal policies toward monopoly and the distribution of income. The views expressed herein are those of the authors and not necessarily those of...

The views expressed in this paper are those of the authors and do not necessarily represent those of the IMF or IMF policy. The consequences for the proper conduct of monetary policy of the existence of a lower bound of zero for overnight nominal interest rates has recently become a topic of lively interest. In Japan, the call rate (the overnight cash rate that is analogous to the federal funds rate in the U.S.) has been within 50 basis points of zero since October 1995, so that little room for further reductions in short-term nominal interest rates has existed since that time, and has been essentially equal to zero for most of the past four years. (See Figure 1 below.) At the same time, growth has remained anemic in Japan over this period, and prices have continued to fall, suggesting a need for monetary stimulus. Yet the usual remedy — lower short-term nominal interest rates — is plainly unavailable. Vigorous expansion of the monetary base (which, as shown in the figure, is now more than twice as large, relative to GDP, as in the early 1990s) has also seemed to do little to stimulate demand under these circumstances. The fact that the federal funds rate has now been reduced to only 1.25 percent in the U.S., while signs of recovery remain exceedingly fragile, has led many to wonder if the U.S.

∗ Preliminary draft. Prepared for the November 2002 Carnegie-Rochsester conference. [Thanks.] The opinions expressed are those of the author and do not necessarily reflect views of the Board of Governors of the Federal Reserve System. 1