Rational Speculators, Contrarians, and Excess Volatility

The VAR approach for testing present value models is applied to a heterogeneousagent asset pricing model, using historical observations of the S&P500 index. Besides rational long-term investors, that value assets according to expected dividends, the model features rational and contrarian speculators. Agents choose their strategy based on evolutionary considerations. Supplementing the standard present value model with speculative agents dramatically improves the model’s ability to replicate the observed market dynamics. In particular the existence of contrarians can explain some of the most volatile episodes including the 1990s bubble, suggesting this was not a rational bubble.