When companies like Aetna or UnitedHealthcare want to rein in costs, they turn to EviCore, whose business model depends on turning down payments for care recommended by doctors for their patients.

The biggest player is a company called EviCore by Evernorth, which is hired by major American insurance companies and provides coverage to 100 million consumers — about 1 in 3 insured people. It is owned by the insurance giant Cigna.

A ProPublica and Capitol Forum investigation found that EviCore uses an algorithm backed by artificial intelligence, which some insiders call “the dial,” that it can adjust to lead to higher denials. Some contracts ensure the company makes more money the more it cuts health spending. And it issues medical guidelines that doctors have said delay and deny care for patients.