I argue that the reason the book-to-market effect is stronger in small stocks is because smaller stocks generally have shorter life expectancy and therefore shorter equity duration. I build a model in which the book-to-market effect is stronger in stocks with shorter life expectancy. Empirically, I use delisting probability as my proxy for life expectancy. The data support my model's central prediction and its additional implications for stock return and variance. My results provide a rational explanation for the heterogeneity of the book-to-market effect, evidence previously taken as support for behavioral explanations.

Abstract We study whether the constraints on firms’ operations imposed by labor unions affect firms’ costs of equity. The cost of equity is significantly higher for firms in more unionized industries. This effect holds after controlling for several industry and firm characteristics, is robust to endogeneity concerns, and is not driven by omitted variables. Moreover, the unionization premium is stronger when unions face a more favorable bargaining environment and is highly countercyclical. Unionization is also positively related to various measures of operating leverage. Our findings suggest that labor unions increase firms’ costs of equity by decreasing firms’ operating flexibility.