Disagreement, Speculation, and the Idiosyncratic Volatility

We propose that speculative trading arising from the joint effect of investor disagreement and short-sale constraints plays an important role in explaining the idiosyncratic volatility (IVOL) puzzle, the correlation among IVOL, market beta and trading volume, and the co-movement of IVOL. Empirical tests show that the return spread between high and low IVOL quintile portfolios is closely related to both aggregate and firm-level disagreement. The common IVOL (CIV) factor is strongly correlated with the aggregate disagreement. The correlation between the IVOL effect and disagreement presents mainly among stocks that are more likely to be short-sales constrained. We provide a mechanism that high aggregate disagreement can lead to more firm-level speculative trading, which is consistent with a factor structure in IVOL and positive correlation among stock beta, the IVOL effect, and the trading volume