How do you really know if your doctor, surgeon or hospital is good, bad or somewhere in between?

I frequently speak with large audiences, ranging from CEOs to Stanford business school students.

I often start by asking participants to raise their hands if they receive excellent health care. Each time I ask, about 90% of the hands in the room shoot up. But all the hands come down when I ask, “How do you know?”

When put in that context, people realize how little information they really have about their physician or hospital’s performance.

It’s easy to be fooled by a doctor’s reputation or the elegance of a waiting room. It’s very difficult to assess a doctor’s true skill or performance.

Of course, there are some indicators of a primary care physician or specialist’s basic competency. Board certification is the most reliable measure.

Information on the status of your doctor’s license, residency training and board certifications can be found on a number of sites, including Certification Matters, American Board of Medical Specialties, American Board of Physician Specialties and the American Osteopathic Association.

However, few of us are searching for a doctor who simply meets basic levels of competency.

We can gain insight into a doctor’s bedside manner and style of practice from online sites like HealthGrades, RateMDs.com orYelp.

But if we want to understand the quality of their outcomes, level of clinical expertise and diagnostic acumen, these subjective and anecdotal surveys don’t do the job.

Of course, the doctor-patient relationship is important. But what most patients care about is whether their doctor’s clinical results are better or worse than others.

The answer remains elusive for multiple reasons, some legitimate and some not.

Take an operation like removing your gallbladder through a laparoscope. Over 95% of the time, a surgeon will solve the patient’s problem correctly. The incidence of complication is rather low.

But let’s assume the difference between great and average is 98% complication free versus 95%.

From a statistical perspective, the difference between a great surgeon and an average one is huge (more than double the complication rate). However, nearly all of their patients will experience an uncomplicated outcome. That’s why asking a friend about their experience isn’t very helpful in determining quality.

So, if a friend can’t provide objective, comparative information on the expertise of physicians, what about asking your personal physician for a recommendation?

Although it’s better than asking a neighbor, few physicians have objective knowledge on the results of their colleagues.

Asking a physician might work if all doctors observed each other in the office and the operating room. But they don’t.

Your primary care physician never directly observes the work of a specialist. And sometimes, the doctor’s referral depends more on how nice the specialist is to the referring physician – not the superiority of their results.

How about finding out where your doctor or surgeon went to medical school or whether they have tenure at a local university?

It sounds great in theory but communicates little in reality. What it takes to be accepted to a prestigious university or hired onto a university faculty is different than what it takes to produce the best clinical outcomes.

What gains entry into an Ivy League school or onto a university faculty is the ability to do well on written tests, perform laboratory research and publish papers. It has nothing to do with manual dexterity or an ability to read an x-ray. The two are not opposites, but the correlation to clinical excellence is minimal at best.

So, where can we turn?

Data, not word-of-mouth, informs us that not all hospitals are equal. The Leapfrog Group has done admirable work in separating the best from the rest. Similarly, many states report outcome data on heart surgery and other complex procedures in U.S. hospitals.

In New York state, for example, the results after cardiac surgery are risk-adjusted (that is, corrected for the complexity of patients, severity of illness and other complicating conditions) before they’re published. Hospitals are then ranked by outcomes to help patients select the best from the rest.

But even where quality data exists, patients often don’t use it consistently or at all.

Case in point: When a former U.S. president needed surgery, he chose a hospital that was ranked near the bottom. He suffered a major complication that theoretically might have been avoided had he made a different choice.

Within larger health organizations like university hospitals and integrated delivery systems, we can predict better results from providers that use an electronic medical record (EMR), which provides comprehensive information on each patient 24/7.

Without a comprehensive EMR, doctors experience delays in acquiring a patient’s diagnoses, medications and lab results. This delay compromises quality and, as a result, patients can fall through the cracks.

Whenever possible, patients should ask whether their doctor or hospital uses a health IT system. While more than 80% of hospitals use EMRs, only about half of all doctors are taking advantage.

Patients may also want to be sure the physician they are referred to for treatment has no conflicts of interest.

Today, some physicians continue their close ties to the pharmaceutical and medical device world, which clouds independent judgment.

That’s why the Federal Government passed the Sunshine Act, which requires public reporting of all payments to health care professionals and teaching hospitals. The information will be available in a public database beginning this September.

In the meantime, ProPublica has already compiled payment information made public by pharmaceutical and medical device companies into a single database.

The reality of this myth is that there is no simple way to assess a doctor’s skill or clinical outcomes.

That’s why more and more patients are gravitating to large medical groups, which are filled with physicians who work closely with each other on a daily basis, observe each other’s work directly and evaluate their colleagues frequently.

When we look at published results from organizations like the National Committee for Quality Assurance (NCQA), Consumer Reports and the Medicare Advantage Star program, we see the same health care organizations at the top of the list more often than not.

Over the next few years, this type of information will become increasingly available. Wise patients will pay greater attention to the data to increase their odds of obtaining the best possible care.

There is a tendency today for us to believe we have the best doctors and health care available. After all, we chose them. But once again, what seems logical only serves to shine a light on another medical myth.

Robert Pearl is a physician and CEO, The Permanente Medical Group. This article originally appeared on Forbes.com.