Why does higher variability of trading activity predict lower expected returns?

The paper shows that controlling for the aggregate volatility risk factor eliminates the puzzling negative relation between variability of trading activity and future abnormal returns. I find that variability of other measures of liquidity and liquidity risk is largely unrelated to expected returns. Lastly, I show that the low returns to firms with high variability of trading activity are not explained by liquidity risk or mispricing theories.