Bigger is thought to be better in these days of health care consolidations and partnerships. Size brings the bargaining power—and the range of patient service—needed to drive down costs and to better coordinate care, improving quality. So goes the mantra uttered time and time again as hospitals and physician practices that once operated independently seek the protection of deep-pocketed partners. But whether this trend will translate into lower cost—particularly for patients—is theoretical at best, experts say. "Have you ever seen costs go down in health care? Anywhere? For anything?" said Glenn Melnick, a health economist at the nonpartisan RAND Corp.