After years of scary, rocket-like growth, America's health care spending has slowed to record lows. That much we know for certain. What's less clear is why -- the weak economy or cost-control measures, including the earliest provisions of the Affordable Care Act. Since health care spending is a major driver of the federal deficit, that's a pretty critical question. The experts at the Kaiser Family Foundation and Altarum Institute are among the first to tease out how much each factor contributed to the slowdown. Their conclusion: about three-quarters is due to the lackluster economy. The rest stems from efforts to keep spending down, including measures introduced in the 2010 "Obamacare" law.