AMERICANS spent $2.6 trillion on health care in 2010, a staggering 18% of GDP. Yet few of them have the faintest idea what any treatment costs or how it compares with any other treatment. Prices vary wildly and seemingly without reason (see chart). Insurance terms require a dictionary. For most Americans, buying a procedure is akin to choosing a house blindfolded, signing a mortgage in Aramaic, then discovering the price later. Slowly, however, this is changing.

The past decade has seen a shift in how people pay for medicine. Americans’ health spending is growing at a slower pace. This is partly because of the downturn, but not entirely. The rate of growth fell every year between 2002 and 2009, note David Knott and Rodney Zemmel of McKinsey & Company, a consultancy. There are many reasons for this—for example, many costly drugs have lost their...