Hospital prices for inpatient services increased more than the prices paid to doctors providing these services between 2013 and 2017, according to a new data brief by United Health Group.

By the numbers: Hospital prices for inpatient services increased by 19% over this time period, or by 4.5% per year. Physician prices for inpatient services increased by 10%, or 2.5% per year.

Yes, but: Part of insurers' job is to negotiate good rates for their enrollees, raising the question of how hospitals are able to cut such lucrative deals year after year.

Insurers say their hands are tied by hospitals with ever-increasing market share, a result of consolidation. This also gives hospitals power over the physicians working in them.

By the numbers: Privately insured patients paid more than $200 billion for hospital inpatient services in 2018, according to the brief.

This number is expected to rise to more than $350 billion in 2029.

Go deeper: Hospitals are swimming in cash