Studies, which some believe could greatly impact future Medicaid budgeting decisions, found that the number of Americans without health coverage may be overstated by as much as 20%.

The Census Bureau estimated that 45 million Americans lacked health insurance for all of 2003. However, actuarial Research Corp., a private company commissioned by the Bush administration, found an estimated 9 million of the 45 million had coverage.  Another estimate, using 2001 data, and calculated by researchers at the Urban Institute, a nonpartisan group, showed an over-count of about 4 million.

Both studies claim that technical problems with the Census Bureau’s Current Population Survey may have resulted in the overstatement in the number of uninsured because of how Medicaid beneficiaries were under counted. Figures from two different Census Bureau surveys estimate Americans without a full year of health coverage range anywhere from 19 million to 45 million for 2003.

The implications of the discrepancy could cause a shift in states’ shares of federal Medicaid dollars, according to some experts. Still, both sets of researchers caution that any lowering of the number of uninsured is likely to be brief, as the erosion of private coverage signals a continued rise in the number of Americans without health coverage.