To the Editor.
—In their recent article on primary care services in the United States, Franks et al1 make reference to the "almost 40 million uninsured Americans" for whom access may be provided under health insurance reform. The total number of uninsured has been quoted as anywhere between 30 million and 40 million, with 37 million being the figure most commonly used. Since this number is often used without any reference or citation, we became interested in where that number came from.Each year, the US Census Bureau conducts its Current Population Survey (CPS) to collect information from the prior year, based on a nationally representative sample of 60 000 households. It would appear that this survey is the most frequently cited source for estimates of the number of uninsured Americans. However, other surveys, such as the Survey of Income and Program Participation (SIPP) and the National Medical Expenditure