UnitedHealth Group is testing a new model of healthcare that many policy experts say holds great promise but has yet to prove itself. Under the medical home model, the insurer will try giving doctors more authority and money than usual in return for closely monitoring their patients' progress, even when patients go to specialists or require hospitalization. The insurer will also move away from paying doctors solely on the basis of how many services they provide, and will start rewarding them more for the overall quality of care patients receive.