We measure organizational concentration—the distribution of a patient's healthcare across organizations—to examine how firm boundaries affect healthcare efficiency. First, when patients move to regions where outpatient visits are typically concentrated within a small set of firms, their...

Patients often receive healthcare from providers spread across different firms. Transaction costs, imperfect information, and other frictions can make it difficult to coordinate production across firm boundaries, but we do not know how these challenges affect healthcare. We define and measure...