Even before the Centers for Medicare & Medicaid Services finalized its shared savings program in October, the concept of accountable care was gaining traction in the marketplace. Combing through news releases, media reports, data from trade associations, interviews and other sources, Leavitt Partners identified 164 ACOs as of September. Leavitt Partners, which is fronted by former Health & Human Services Secre- tary Michael Leavitt, found that 99 of the organizations primarily were sponsored by a hospital or health system, 38 by physician groups and 27 by insurers. Here are five key trends Leavitt Partners found:

1. Dispersion of ACOs varies by market. Much of the ACO growth seems to be reactionary: where one exists, competitors follow suit.

2. Some regions are devoid of an ACO. Poorer and rural regions show little ACO growth.

3. Hospitals and health systems are the primary forces behind ACOs. Nearly two-thirds of ACOs identified by the research were started by a hospital or health system. But with insurers and physician groups charting their own ACO courses, there are "many different models of providing care for a patient population."

4. Significant investments in ACOs exist independent of Medicare's shared savings program. With the Medicare shared savings program in its infancy, private-sector initiatives are driving growth thus far.

5. The success of different ACO models is unproven. "While there are different models of providing accountable care, which approaches are most successful at realizing an ACO's goal is still unclear."

The report also notes: "Preliminary review of organizations we have identified indicates a trend toward proclaiming oneself as an ACO with only modest changes to the care process, rather than radically redesigning the organization to become something fundamentally different in the future."

To view a copy of the full report, visit http://leavittpartners.com.