The National Institute of Health Care Management has a new brief out that explores the factors driving up health-care spending, trying to explain why premiums have grown by 122 percent over the past decade.

The answer, at least in recent years, can be summed up in one word: Prices. The volume of health care that Americans used actually dropped between 2009 and 2010, then grew slightly between 2010 and 2011.

The column to the left of all these bar charts show overall health-care spending increases. Unsurprisingly, health-care costs have been rising. Pretty much all of that has been driven by the cost of each unit of health care, the price tag on an MRI, for example, or a trip to the doctor. 

The actual amount of health care we get, the trips to the doctor or visits the the MRI, has held steady or even fallen. The number of outpatient visits, for example, dropped by 4.2 percent between 2010 and 2011.

When we talk about our health spending problem, these charts suggest that it's less about the volume of health care delivered and more about the cost of each service.