We develop a simple approach to valuing stocks in the presence of learning about average profitability. The market …-to-book ratio (M/B) increases with uncertainty about average profitability, especially for firms that pay no dividends. M/B is … returns. Firm profitability has become more volatile recently, helping explain the puzzling increase in average idiosyncratic …

investment models must be attributable to movements in equity risk premia. In this Paper we emphasise that such movements in … equity risk premia should have implications not merely for investment today, but also for future investment over long …-horizon fluctuations in the growth of marginal Q, and therefore investment. We test this implication directly by performing long …