America's hospitals are the most expensive part of the world's most expensive health system. They accounted for $851 billion, or 31%, of American health spending in 2011. If they were a country, they would be the world's 16th-largest economy. And they are in the midst of dramatic change, much of it due to the "Obamacare" health reforms. The most visible change so far is that big hospital companies are getting bigger. In the latest of a string of recent mergers and takeovers, on June 24th Tenet Healthcare said it would buy Vanguard Health Systems for $4.3 billion including debt. The combined group will have 79 hospitals and 157 outpatient clinics.