As nurse practitioners lobby to expand their authority and scope of practice in many states, a New England Journal of Medicine study released Wednesday documents a deep chasm between doctors and nurses on that issue. The study found the two groups overwhelmingly agreed that nurse practitioners should be able to practice to the full extent of their schooling and training. But doctors were less likely to concur that advanced practice nurses should lead medical homes, which deliver team-based, coordinated care to patients. Only 17 percent of the 505 primary care physicians surveyed agreed with that notion, compared to 82 percent of the 467 nurse practitioners surveyed.