Primary care: a critical review of the evidence on quality and costs of health care.

Despite contentious debate over the new national health care reform law, there is an emerging consensus that strengthening primary care will improve health outcomes and restrain the growth of health care spending. Policy discussions imply three general definitions of primary care: a specialty of medical providers, a set of functions served by a usual source of care, and an orientation of health systems. We review the empirical evidence linking each definition of primary care to health care quality, outcomes, and costs. The available evidence most directly supports initiatives to increase providers' ability to serve primary care functions and to reorient health systems to emphasize delivery of primary care.