Navigating the health care system in the United States can often feel like being lost in a maze. What kind of doctor should I see? Who takes my insurance? What even is a co-pay, anyway?

For that reason, Chris Hamby, an investigative reporter, has devoted much of his five-year career at The New York Times to guiding readers through such dizzying questions. His latest article, which was published online this month, explored the complex subject of insurance bills.

Last year, Mr. Hamby began investigating MultiPlan, a data firm that works with several major health insurance companies, including UnitedHealthcare, Cigna and Aetna. After a patient sees an out-of-network medical provider, the insurer often uses MultiPlan to recommend how much to reimburse the provider.

Mr. Hamby’s investigation revealed that MultiPlan and the insurers are incentivized to reduce payments to providers; in doing so, they score larger fees, which are paid by the patient’s employer. Many patients are forced to foot the rest of the bill. (MultiPlan said in a statement to The Times that it uses “well-recognized and widely accepted solutions” to promote “affordability, efficiency and fairness” by recommending a “reimbursement that is fair and that providers are willing to accept in lieu of billing plan members for the balance.”)

In an interview, Mr. Hamby shared his experience poring over more than 50,000 pages of documents and interviewing more than 100 people. This conversation has been edited.

Where did your investigation begin?

We were broadly looking at issues in health insurance last year. MultiPlan kept coming up in my conversations with physician groups, doctors and patients. At first, it was unclear what exactly MultiPlan did. There were some lawsuits regarding its work with UnitedHealthcare, but it was difficult to understand the company’s role in the industry. We eventually accumulated more information about MultiPlan’s relationship with big insurance companies.