Employer-based health insurance starts at the turn of the century and is prevalent by the 1950s. Due to rising access to healthcare and other factors, hospital use goes up, and costs related to care increase.
To limit unnecessary stays and cut costs, hospital physicians begin peer-based “medical necessity” checks, but don’t have the tools or resources to standardize them. Insurers — highly invested in reining in costs — step in, and as insurance companies multiply, so do their custom review processes. By 2018, these have grown to encompass treatment, procedures, and medications, sparking controversy over who should decide what is “medically necessary” for patients — physicians or payers.