Learning asymmetries in real business cycles$

When a boom ends, the downturn is generally sharp and short. When growth resumes, the boom is more gradual. Our explanation rests on learning about productivity. When agents believe productivity is high, they work, invest, and produce more. More production generates higher precision information. When the boom ends, precise estimates of the slowdown prompt decisive reactions: investment and labor fall sharply. When growth resumes, low production yields noisy estimates of recovery. Noise impedes learning, slows recovery, and makes booms more gradual than downturns. A calibrated model generates growth rate asymmetry similar to macroeconomic aggregates. Fluctuations in agents’ forecast precision match observed countercyclical errors of forecasters. ‘‘There is, however, another characteristic of what we call the trade cycle that our explanation must cover; namely, the phenomenon of the crisis—the fact that the substitution of a downward for an upward tendency often takes place suddenly and violently, whereas there is, as a rule, no such sharp turning point when an upward is substituted for a downward tendency.’’ J.M. Keynes (1936) r 2006 Elsevier B.V. All rights reserved