The idea that spending more on preventive care will reduce overall health care spending is widely believed and often promoted as a reason to support reform. It’s thought that too many people with chronic illnesses wait until they are truly ill before seeking care, often in emergency rooms, where it costs more. It should follow then that treating diseases earlier, or screening for them before they become more serious, would wind up saving money in the long run.

Unfortunately, almost none of this is true.

Let’s begin with emergency rooms, which many people believed would get less use after passage of the Affordable Care Act. The opposite occurred. It’s not just the A.C.A. The Oregon Medicaid Health Insurance experiment, which randomly chose some uninsured people to get Medicaid before the A.C.A. went into effect, also found that insurance led to increased use of emergency medicine. Massachusetts saw the same effect after it introduced a program to increase the number of insured residents.

Emergency room care is not free, after all. People didn’t always choose it because they couldn’t afford to go to a doctor’s office. They often went there because it was more convenient. When we decreased the cost for people to use that care, many used it more.

Wellness programs, based on the idea that we can save money on health care by giving people incentives to be healthy, don’t actually work this way. As my colleague Austin Frakt and I have found from reviewing the research in detail, these programs don’t decrease costs — at least not without being discriminatory.