Working Paper: NBER ID: w17301
Authors: Andreas Fuster; Benjamin Hebert; David Laibson
Abstract: How does an economy behave if (1) fundamentals are truly hump-shaped, exhibiting momentum in the short run and partial mean reversion in the long run, and (2) agents do not know that fundamentals are hump-shaped and base their beliefs on parsimonious models that they fit to the available data? A class of parsimonious models leads to qualitatively similar biases and generates empirically observed patterns in asset prices and macroeconomic dynamics. First, parsimonious models will robustly pick up the short-term momentum in fundamentals but will generally fail to fully capture the long-run mean reversion. Beliefs will therefore be characterized by endogenous extrapolation bias and pro-cyclical excess optimism. Second, asset prices will be highly volatile and exhibit partial mean reversion--i.e., overreaction. Excess returns will be negatively predicted by lagged excess returns, P/E ratios, and consumption growth. Third, real economic activity will have amplified cycles. For example, consumption growth will be negatively auto-correlated in the medium run. Fourth, the equity premium will be large. Agents will perceive that equities are very risky when in fact long-run equity returns will co-vary only weakly with long-run consumption growth. If agents had rational expectations, the equity premium would be close to zero. Fifth, sophisticated agents--i.e., those who are assumed to know the true model--will hold far more equity than investors who use parsimonious models. Moreover, sophisticated agents will follow a counter-cyclical asset allocation policy. These predicted effects are qualitatively confirmed in U.S. data.
Keywords: Natural Expectations; Macroeconomic Dynamics; Asset Pricing
JEL Codes: D84; E32; G12
Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| agents' belief systems (D83) | economic behavior (D22) |
| natural expectations (D84) | endogenous extrapolation bias (C51) |
| endogenous extrapolation bias (C51) | overly optimistic beliefs during economic booms (E32) |
| endogenous extrapolation bias (C51) | overly pessimistic beliefs during downturns (E32) |
| past performance (C52) | current asset pricing (G19) |
| shocks to consumption (E21) | delayed and persistent effects on consumption growth (E21) |
| agents' perception of equities as riskier (G12) | large equity premium (G12) |
| knowledge of the economic model (E10) | countercyclical asset allocation (G11) |
| natural expectations (D84) | procyclical behavior (E32) |