Offering a rare glimpse inside the hidden world of rejected insurance claims, new data shows a steady uptick among major private insurers.

Prescription drug denials by private insurers in the United States jumped 25 percent from 2016 to 2023, according to a new analysis of more than four billion claims, a practice that has contributed to rising public outrage about the nation’s private health insurance system.

The report, compiled for The New York Times by the medical data company Komodo Health, shows that denial rates rose from 18.3 percent to 22.9 percent. The rejections went up across many major health plans, including the country’s largest private insurer, UnitedHealthcare.

The data offers a rare look into the largely hidden world of rejected insurance claims. While some government-funded health plans are required to publish their denial rates, most private insurers keep that information confidential. Komodo draws from private databases that collect denial details from pharmacies,