"When you have a very challenging population, and you don't have all those levers, you might say to yourself, 'We don't have these tools we need in this contract to be financially sustainable.' I think that is the case for multiple ACOs in both of the Medicare programs, and it will likely be the case for a lot of ACOs that don't have the ability to pull those levers."

Regarding the health IT infrastructure that ACOs need to be successful, Cassels acknowledged that the collection and reporting of quality data has been a challenge for ACOs, as it has been for providers trying to show Meaningful Use. The key problem is that the data generated by electronic health records is not reliable for this purpose and it takes a lot of time to collect the data manually.

"It's a big problem to be spending a disproportionate amount of time and focusing clinicians' attention on records and data abstraction," he said. "When your vision is on care redesign and quality improvement and you have to spend a lot of time and money on systems to send data files to the federal government to watch over your shoulder, that's frustrating to many physicians and administrators."

Some Pioneer ACOs also have a problem with the method that CMS is using to benchmark their quality data. Since this was reported back in February, CMS has reportedly agreed to revise the benchmark methodology, but talks are said to be continuing.

It has also been reported that some of the Pioneer ACOs were upset about the six-month lag in the Medicare claims data that CMS was giving them. Asked about this, Cassels said that, across the healthcare industry, both providers and payers fantasize that having each other's data will solve many of their problems.

"What has become very clear to the folks in the Medicare shared savings and the Pioneer program is not only that there isn't that pot of gold at the end of the rainbow, but putting that pot of gold together with ours is pretty challenging." In other words, he said, claims and clinical data are like apples and oranges when it comes to getting useful information by combining them.

Even the organizations most experienced in population health management, such as Kaiser Permanente, Geisinger Health System and the University of Pittsburgh Medical Center, don't have all the answers, Cassels said. Considering what a steep learning curve other organizations will have in moving to this form of care delivery from "reactive sick care," he concluded, it's clear that not everybody will make it. "Some folks just don't have the capacity to be successful with this strategy."