This article examines a dynamic adverse‐selection model that generates equilibrium employment cycles. In the model, firms hire workers from unemployment, observe workers' productivity through time, and (following the profit‐maximizing rule) eventually fire unproductive workers. If hiring costs are low, the dynamical system converges to a steady state in which the unemployment pool contains mostly low‐ability workers. However, if hiring costs are sufficiently large, this “lemons effect” would make firms unwilling to hire workers. In this case, the system converges to a cyclical equilibrium in which firms alternate between hiring and not hiring.

Using Tobin's q as a measure of performance, we seek to estimate the relative importance of industry, focus, and share effects in determining firm performance. Our methods are analogous to those of Richard Schmalensee and, like him, we find that industry effects account for the majority of the explained variance. However, we also find that firm effects exist in the form of focus effects, that is, narrowly diversified firms do better than widely diversified firms. We interpret this finding as consistent with profit maximization by firms with different factor endowments.

Using Tobin's q as a measure of performance, we seek to estimate the relative importance of industry, focus, and share effects in determining firm performance. Our methods are analogous to those of Richard Schmalensee and, like him, we find that industry effects account for the majority of the explained variance. However, we also find that firm effects exist in the form of focus effects, that is, narrowly diversified firms do better than widely diversified firms. We interpret this finding as consistent with profit maximization by firms with different factor endowments.