On Tuesday, the federal government released a massive amount of data showing how much it paid the vast majority of doctors who treated Medicare patients in 2012.

The thing it doesn't show? Whether that was $77 billion well spent.

One percent of doctors got more than 15 percent of Medicare payments

One percent of the 880,000 medical providers included in this study netted more than 15 percent of all Medicare payments in 2012, according to the New York Times' analysis of the data. That means fewer than 9,000 doctors managed to make more than $11 billion off Medicare.

That's an incredible concentration figure. The question is whether it represents great doctors meeting demand for their terrific work or providers who are bilking the system or overtreating their patients.

"Some of the scrutiny of the highest of the highest paid will focus on overuse," says Ethan Halm, a professor at the University of Texas Southwestern Medical Center, whose research focuses on health care quality. "If these small handful of eyeball surgeons are the highest paid, that could be a harbinger of overuse.

"But should we be surprised if the world's best pancreatic surgeon makes a lot per case, and does a lot of cases?"

What's new here: for the first time, we know what doctors actually spend their day doing

By combing through the things that doctor asks Medicare to pay them for, you can see what your doctor is up to each day. (Yes, your doctor! The Wall Street Journal has a searchable database here.)

"If I'm an internal medicine doctor, you might come to me for anything imaginable," says Bob Kocher, a former health-care advisor to the White House. "Some poor psoriasis patient might come to me, and I've only seen seven people with psoriasis. Now, as a patient, you'll be able to use this data – or at least use tools built with this data – to know what does the doctor I'm about to visit actually do."

We have no idea why some doctors earn so much money

Seriously. No idea. This is the most important take away.

We do know huge variation in how much Medicare paid doctors in 2012. The highest-earning doctor was an ophthalmologist in West Palm Beach, Fla. who earned just shy of $21 million seeing 894 patients. The lowest-paid provider was an osteopath in Arizona who appears to have earned $2.29 (possibly a reconciliation payment to claims submitted last year).

Experts say we should be skeptical of the outliers, the people who say they're seeing way more patients than anyone else in their specialty. "If you're doing 100 times more of a procedure than any other doctor, that's a red flag," says Jennifer Schneider, who runs strategic analytics at transparency firm Castlight Health.

But for most other doctors, this data doesn't tell us whether high-earners are standouts in their profession — people who excel at complex surgeries, for example — or if they're bilking the system.

Should any one doctor really be earning $21 million from Medicare?

Probably not. That ophthalmologist who was Medicare's highest-earner in 2012? He was under investigation for fraud in January 2013.

That's an outlier case, of course. But the Times also found that the top 100 earners netted a collective $610 million. Those are the doctors that are likely to draw more federal scrutiny.

Medicare's Jonathan Blum says that his agency was looking at providers who tend to be the highest-earners.

"There are certain physicians who are renowned experts who should see more volume," he told reporters on a Tuesday call. "There is some spending that appears to be wasteful, or could be fraudulent. Our goal is to ask those types of questions."

In other words: Medicare's top earners are likely really great doctors – or they might be criminals. We don't know which quite yet.

When a doctor sees tons of patients, that could be great – or terrible – news

There's a lot of research showing that doctors who perform more of a specific medical procedure tend to have the best patient outcomes, especially when it comes to the really complex ones.

"We know that for unusual or high risk procedures, high volume is associated with better outcomes," Halm of UT-Southwestern says.

But this can also lead to something Halm describes as a "practice makes perfect" problem: the doctors delivering these really great results might be over-treating their patients, essentially practicing on people where the medical guidelines don't recommend treatment.



