Three of the nation’s largest insurance companies – Aetna, Humana and UnitedHealth – have let researchers have a look at the negotiated prices they pay for services and procedures like C-sections, MRIs and hospital stays. This includes claims data for 88 million customers and $682 billion of healthcare bills. For a long time, economists like Martin Gaynor have believed the more hospitals merge, the more their monopoly power helps them drive prices up. Until now though, the evidence has been limited to single states or hospitals that have merged and it often relied on the sticker price listed by hospitals. This analysis is different because it comes from hospitals coast to coast and uses the actual amount insurers paid.