When Massachusetts policy makers began crafting a healthcare initiative, there were 460,000 uninsured people living in the state. Or was it 748,000?
The first number was the state's estimate; the second was from the US Census Bureau. The reality was probably somewhere in between, and the difference explains - in large part - why the state is faced with spending hundreds of millions more to subsidize health insurance than it expected.
Each of the two official estimates was known to be flawed.
The state survey is widely believed to undercount uninsured residents because it is based on phone interviews, which miss those with only cellphones and other individuals more likely to be uninsured. The Patrick administration is revamping the surveying strategy for this year's estimate.
Specialists believe the census overcounts the problem in Massachusetts, because it misses some people who have Medicaid coverage and because it uses national averages to fill in missing information.
The Legislature worked with a third number, between the other two, and projected that 215,000 of the uninsured would ultimately qualify for state-subsidized coverage.
By October 2006, when the state began enrolling low- and moderate-income people in the subsidized-coverage program known as Commonwealth Care, a new state estimate predicted that 140,000 to 160,000 residents would sign up.
But enrollment surged. By the beginning of this year, 169,000 people had enrolled. And the state now projects that the total may reach 342,000 by 2011.
John Holahan, director of health policy research at the Urban Institute, who has studied the uninsured in Massachusetts, said neither the recent enrollment surge nor the expected future growth surprise him.
"I don't think people are coming out of the woodwork and taking advantage of the system," said Holahan. "I think they were there all along."