We show that a necessary and sufficient condition for entry to be unprofitable in markets with adverse selection is that that no buyer type be willing to trade at a price above the expected unit cost of serving those types who are weakly more eager to trade than her. We provide two applications...

Many econometric models used in applied work integrate over unobserved heterogeneity. We show that a class of these models that includes many random coefficients demand systems can be approximated by a “small-σ” expansion that yields a linear two-stage least squares estimator. We study in...

Many econometric models used in applied work integrate over unobserved heterogeneity. We show that a class of these models that includes many random coefficients demand systems can be approximated by a "small-o" expansion that yields a straightforward 2SLS estimator. We study in detail the...

Many econometric models used in applied work integrate over unobserved heterogeneity. We show that a class of these models that includes many random coefficients demand systems can be approximated by a "small-σ" expansion that yields a linear two-stage least squares estimator. We study in...