Paying a Premium on Your Premium? Consolidation in the US Health Insurance Industry
研究美国健康保险行业整合是否推高了雇主提供的保险保费，利用两家保险公司全国合并的差异影响识别因果关系，发现1998-2006年间本地集中度上升导致2007年平均保费提高约7个百分点，并发现整合增强了买方垄断势力，降低了医生的就业和收入。
We examine whether and to what extent consolidation in the US health insurance industry has contributed to higher employer-sponsored insurance premiums. We exploit the differential impact across local markets of a national merger of two insurers to identify the causal effect of concentration on premiums. Using data for large groups, we estimate premiums in average markets were approximately seven percentage points higher by 2007 due to increases in local concentration from 1998–2006. We also find evidence consolidation facilitates the exercise of monopsonistic power vis-à-vis physicians, leading to reductions in their absolute employment and earnings relative to other healthcare workers.