“What kind of insurance you have does affect your access to health care,” said Carrie Colla, associate professor of the Dartmouth Institute for Health Policy & Clinical Practice and the lead author of the study. “But once you’re in front of the doctor, by and large you’re treated the same way as any other patient.”

One apparent exception found in the study involved the seventh service it examined: cardiac testing before low-risk, noncardiac surgery. This service was provided to 46 percent of Medicare beneficiaries and 26 percent of privately insured patients. The large difference could reflect the fact that cardiac problems are more prevalent among older people. So a doctor with equal concern for all her patients might test Medicare patients at a higher rate for that reason. Nonetheless, such testing is considered low value even for the Medicare population.

Another recent study, published in JAMA Internal Medicine, also found little relationship between insurance status and low-value care. The study found no difference in the rates at which seven of nine low-value services were provided to patients on Medicaid versus those with private coverage. Six were also provided at the same rates for uninsured and privately insured patients.

Moreover, the study found that physicians who see a higher proportion of patients on Medicaid provide the same rate of low- and high-value services for all their patients as other physicians do. This is an important finding because Medicaid pays doctors less than private plans do, raising concerns that higher-quality doctors would tend not to participate in the program.

“Despite concerns to the contrary, Medicaid patients don’t appear to be seeing lower-quality doctors,” said Dr. Michael Barnett, lead author of the study, a physician with the Brigham and Women’s Hospital and an assistant professor at the Harvard T.H. Chan School of Public Health. “Though raising the prices Medicaid pays doctors may increase physician participation, enhancing enrollees’ access to care, it isn’t likely to change the quality of care patients receive once they are in the doctor’s office.”

If insurance status doesn’t influence how much low-value care patients are being offered, what does? In part, it seems related to the history and organization of local health care markets. A big culprit, according to Ms. Colla’s study, is a market’s ratio of specialists, like cardiologists and orthopedists, to primary care physicians. In areas where there are relatively more specialists, there is also more low-value care. That’s not to say that specialists don’t provide valuable services — but it suggests that they tend to provide more low-value care as well.

In a way, this is good news — the medical system doesn’t seem to discriminate by insurance status. It also means that public programs appear to be relatively cost-efficient, spending less than private payers for care of similar quality. That bodes well for Democrats’ proposals to expand Medicare or Medicaid.

But the bad news is that the study results imply that the value of care is hard to influence by adjusting prices. In a normal market, paying less for something would send a message of its low value, prompting people to provide less of it. The fact that price apparently does not influence doctors’ decisions is just another way in which health care does not seem to function like other markets.