Ask a physician why he prescribes unnecessary tests or treatments, and he’s likely to say he’s responding to demands from his patients (or trying to avoid a lawsuit). But a new study in the journal  JAMA Oncology finds that perception may be wildly wrong.

The study, by Keerthi Gogineni, Katherine L. Shuman, Derek Chinn, Nicole B. Gabler, and Ezekiel  Emanuel found that patients asked for a specific test or treatment in less than 10 percent of visits, and that nearly 9 in 10 of those requests were medically appropriate. In short, patients demanded what their physicians considered inappropriate care only about 1 percent of the time.

The authors interviewed 60 medical professionals at three hospital-based outpatient oncology clinics in Philadelphia in 2013 and 2014. Those clinicians described more than 5,000 encounters with 3,600 patients. And they reported that in those 5,000 visits, patients requested a specific medical intervention just 440 times. About two-thirds of those demands were for an imaging study or lab test. Strikingly, about 15 percent were for palliative care—where patients were explicitly requesting less aggressive treatment.

Only about 17 percent requested a specific therapy. Of those, fewer than 4 percent asked to be put in a clinical trial or on an experimental drug. The clinicians surveyed reported only about 4 percent of those treatment requests were inappropriate.

Where did patients get the information they used to request treatment? If you said the Internet, you’d be wrong. One-third came from other doctors; about 40 percent from family, friends, or fellow patients; and about 7 percent from medical reference books. Less than 14 percent told their physicians they got their information on the Web, although one in five of the inappropriate requests were based on online material.

Remarkably, less than one percent reported they responded to advertising. The surveyed clinicians said that in about half the cases, they did not know where their patients got their advice.

The researchers found no significant differences between patients who demanded treatment and those who did not, with one exception. Race, sex, age, insurance coverage, income, and the like did not seem to matter.

The study did oversample cases involving high-income patients with insurance. And, of course, was limited to cancer patients in Philadelphia. However, these patients may well be more demanding than average.

If patient demographics didn’t matter, what did? The patient’s relationship with her doctor. Only about 8 percent of those who had a good or excellent relationship proactively requested care, but three times as many with a fair or poor relationship did so. Trust matters.

But if the demanding patient is a myth, at least among oncology patients in Philadelphia, why are so many physicians convinced they are a problem? Other studies report that between 40 percent and 66 percent of docs say they have had patients demand specific treatment.

The researchers have no data. But they suggest those requests, while infrequent, may stick in a doctor’s mind because physicians find them threatening and because they are time-consuming to address. And, perhaps, the researchers say, doctors feel they may have acted unprofessionally by complying with requests they knew to be inappropriate.

But whatever drives the perception, there are two take-aways from this study:

1) Doctors who order that extra test or push for one more treatment may be doing so because they want to, not because they are being asked by the largely mythical demanding patient.

2) As a patient, if you do think some therapy may be appropriate by all means ask your doctor about it. You may not want to demand a specific treatment, but you should always talk about it.