We asked experts for their opinions on various approaches to attribution, including attribution to single versus multiple organizations, prospective versus retrospective attribution, and attribution to integrated versus virtual groups of providers. The area where the experts expressed the strongest opinions was on prospective versus retrospective attribution, where they had differences of opinion. Some experts strongly believed that providers would not "buy in" to episode-based approaches unless they had, at the outset, identified the patients/episodes for which they were accountable, similar to the Medicare Physician Group Practice demonstration model. One expert stated that providers were comfortable with this approach since this was consistent with how they viewed patient care - although they are currently paid per service, they don't tend to think in terms of individual services but rather from when a patient presents with a particular condition until the point where treatment stops. Other experts expressed a concern that very few providers were organized to be able to accept accountability for episodes, and that strong incentives would be required to drive them to organize themselves to do so. Some experts expressed doubts that many providers would voluntarily accept accountability for episodes. These experts favored identifying accountability retrospectively using empirical data, and pointed to studies such as those of "accountable care organizations" of a hospital and associated physicians by Fisher and colleagues as evidence that this approach would be feasible
On a related issue, attribution to real versus virtual groups of providers, there were also differences of opinion. Some experts favored beginning first with allowing integrated provider groups to accept accountability for episodes. Other experts expressed concerns that this would reward existing organizational structures, and that allowing for attribution to virtual groups would allow for more innovation in health care delivery.