In a previous post, I wrote about a new study published in the Annals of Internal Medicine finding the Massachusetts health care law signed by former Gov. Mitt Romney in 2006 led to a measurable reduction in mortality in the state relative to other counties in the United States with similar demographics that did not expand coverage.

But as experts debate how much the Massachusetts experience is likely to be replicated nationally as President Obama's health care law expands the number of Americans with insurance, one question worth exploring is how much of a role the world-class medical system in Massachusetts that existed prior to the passage of Romneycare played in these findings.

The authors of the study themselves note the fact that Massachusetts had the "most per capita physicians in the country" may be one reason why the results may not be generally applicable. So I decided to delve into that a bit more, and I found that according to Census data, in 2006, Massachusetts had 462 doctors per 100,000 residents -- which ranked it as the top state. Maryland came next, with 415. By Michigan, the 25th ranked state, the number dropped to 245. And the bottom state, Idaho, had just 169 doctors per 100,000 residents. Because these numbers are from 2006, the year Romneycare became law, they wouldn't have been affected one way or another by the implementation.

But even this may not tell the whole story, because what matters is not just the raw number of doctors, but the quality of physicians as well as the medical facilities that are available -- the access to life-saving equipment and cutting edge treatments.

And there's reason to believe that Massachusetts is leader on that front, too. For instance, Massachusetts General has consistently ranked as one of the best hospitals in the U.S. It has an annual research budget of over $750 million, which is the largest in the nation for a hospital-based research program.

So it's possible that what the Massachusetts study picked up is not necessarily that increasing health insurance coverage decreases mortality in general, but doing so in an area with a vast pre-existing medical infrastructure with a high concentration of skilled doctors and world-class medical facilities is what makes the difference.

Though this is obviously impossible to say based on the currently available research, as Obamacare gets implemented and expands insurance coverage nationally, one interesting area for future study may be to compare changes in mortality rates in multiple states with expanded coverage, and then see what type of variation there is when considering factors such as the concentration of medical providers.