How much do hospitals and doctors actually charge insurers for their services? How much and which of those services are privately-insured patients using? And, most significantly, what drives changes in health-care use, costs, and total spending?

They are among the most vexing questions in American health care. And a recently amassed trove of data from insurance companies could soon shed new light on them.

Compiled by the non-profit, non-partisan Health Care Cost Institute, the database will allow researchers to slice and dice more than 3 billion medical claims for more than 33 million individuals in search of answers.

The previously confidential information, scrubbed of identifying details, is being provided by three of the nation’s largest insurance companies: Aetna, Humana, and UnitedHealthcare--whose combined customers account for about 20 percent of Americans under age 65 who are insured through an employer.

Until now, researchers have had to extrapolate from far smaller surveys of employers, or rely on government claims statistics from Medicare, which are almost exclusively limited to Americans over age 65.

(The Washington Post/Source: Health Care Cost Institute)

On Monday, the institute offered a first look at its findings, in a report that largely confirmed previously identified trends, but added intriguing details.

For instance, analysts have been puzzling over why, after more than a decade of alarming growth, health-care spending is now rising more slowly.

Institute researchers were able to put numbers to one of the most popular theories: People are using less health-care.

According to the report, from 2009 to 2010 people with employer-sponsored insurance had 3.3 percent fewer admissions to hospitals and other medical facilities, 3.1 percent fewer “outpatient” visits to such facilities, and virtually no change in the number of procedures performed at doctor’s offices. (There was a slight increase in two categories: procedures performed at medical facilities, which went up by 2 percent, and use of prescription drugs, which increased by just under 1 percent.)

“People had speculated that there was a decline in utilization, but by analyzing over 3 billion claims we now know not only the trend but the magnitude of the trend,” said David Newman, the institute’s executive director. “It’s one thing to believe something, it’s a completely different thing to actually know it.”

It is likely that much of the dip in utilization is connected to the recent recession and sluggish recovery. Faced with a loss of income, wealth, or job security, patients could be putting off non-urgent care.

But many analysts argue the drop-off is too significant to be accounted for by economic factors alone. And Monday’s report also fleshed out details of another possible explanation: The rising price patients must pay for care.

In 2010 the average out-of-pocket payment for an admission to a hospital or other facility went up by more than ten percent to $700. The total charge for an outpatient visit--which can include an emergency room visit or surgery that does not require an overnight stay--also rose ten percent, reaching $162.

To some extent, the increases reflected the decision by many employers to push more of the cost of care onto workers in the form of higher deductibles, co-pays, and co-insurance.

But that shift was relatively modest: In 2009, patients paid for 15.6 percent of their care out-of-pocket, in 2010, the figure was 16.2 percent.

Instead, the increased spending by not just patients, but employers was primarily caused by increases in the prices that hospitals, doctors and other providers charged for every category of service in 2010.

The total price per outpatient visit, including both the insurer and the out-of-pocket share, rose the fastest--10 percent to $2,224. The increase was also significant for inpatient admissions, which went up 5.1 percent to $14,662.

Indeed, the researchers found that these price boosts were large enough to offset the impact of not just the dip in utilization but a 0.8 percent decline in the number of people who have employer sponsored plans. As a result, total spending on this population rose by 2.5 percent in 2010.

(Another contributing factor was a continued rise in the “intensity” of care, meaning the complexity--and expense--of services used. But the report’s authors found this was a far less important driver of overall spending than the price increases.)

“I think one of the key things coming out of the report will be to ask the people who are setting prices why are prices going up four to five times the underlying rate of inflation for these services,” said Newman. “There may be a good reason, but this suggests one should at least be asking the question.”

Newman said researchers would also be doing further analysis to try to explain another perplexing finding: The growth in spending per patient in 2010 was as much as twice as high for those 18 and under than for any other age group.

“We’re all fascinated by this, and the question is what are the drivers,” he said. “Do they portend that this [population] is somehow different such that they will have higher costs through their lives--which raises implications about bending the long term cost curve?”

And with another 2 billion in additional claims in the database yet to be analyzed, and plans for a fourth insurer, Kaiser Permanente, to hand over its claims, Newman predicted that scores of outside researchers will soon be using it to answer new questions of their own.