Nearly one in five Americans under the age of 65 were without health insurance in 2005, a number that has continued to increase in the last decade. The demographics of the nearly 45 million uninsured are a mix of people living below the poverty line, young people and others.

Work status and income
"The uninsured are -- and have been for years and years -- mainly people who make less than 200 percent of the poverty level," said Cathy Hoffman, associate director of the Kaiser Commission on Medicaid and the Uninsured. In 2006, that federal poverty level was $20,000 for a family of four.
Poor, however, does not mean unemployed. Nearly 70 percent of the uninsured come from families with at least one full-time worker.

"The uninsured aren't people who are disconnected from employment, but they are disconnected from affordable health insurance -- either because it's not offered by their employer or because the share they're asked to pay is more than they can afford," said Hoffman.

Part-time workers, who are less likely to be offered health insurance, are even more vulnerable. They make up only 19 percent of the population, but 28 percent of the uninsured.

Workers who work for small companies are also more at risk, because those companies are less likely to be able to offer insurance to their employees. Only 52 percent of companies with less than 10 workers offer their employees health insurance, while 99 percent of firms with more than 200 employees do, according to a 2004 Kaiser Foundation study of employer health benefits.

"The profile of the uninsured has not really changed much since we've been studying it," said Paul Fronstin, a senior research associate at the Employee Benefit Research Institute, who's been examining data on the uninsured for more than 15 years. "It's low income workers, it's people in the labor force or associated with someone in the labor force, and it's disproportionately tied to people who work in small businesses."

Age
Thanks in large part to a major federal initiative, one group that's been faring better in recent years is children. Over the past decade, new and expanded government programs such as Medicaid and the State Children's Health Insurance Program have made progress in covering children under age 19. According to a Kaiser Commission study, the percentage of low-income children without health insurance fell by about one-third between 1997 and 2004.

Nevertheless, there are still more than 8 million uninsured children in the United States, Hoffman points out -- and up to three-quarters of those children might be eligible for Medicaid or SCHIP. "The programs are in place, we just need to do a better job of reaching them," Hoffman said.

Adults, meanwhile, have not fared as well. "We know that between 2000 and 2004 ... all of the growth in the number of the uninsured was among adults," said Hoffman.

Young adults are particularly at risk. A 2003 Commonwealth Fund study found that the fastest-growing segment of the uninsured are young adults between the ages of 19 and 29, whose combination of low incomes and unstable jobs make it difficult for them to find and afford health insurance. In 2005, nearly 30 percent of people between the ages of 19 and 24 lacked health insurance. In comparison, less than 20 percent of people between the ages of 35 and 44 were uninsured.

Citizenship
American citizens -- especially native-born citizens -- are much more likely to have health insurance than immigrants are. In 2005, about 13 percent of native-born citizens lacked health insurance, while 43 percent of noncitizens did, according to the census bureau.

Even that estimate might be too low, according to Hoffman, because it's hard for census-takers to find undocumented workers willing to answer survey questions.

While all experts agree that noncitizens are less likely to have health insurance than citizens, the jury is still out on the question of how much impact immigrants have on the overall national uninsured rate.

Hoffman said that the idea that the growth of the uninsured rate is being fueled by immigrants is myth. "The numbers just don't support that," she said. "The large majority of the uninsured are U.S. citizens. While immigrants and the undocumented are less likely to have health insurance, there just aren't enough of them to make a difference in the overall rate."

But Fronstin disagreed. He said that his research found that immigration accounted for about 85 percent of the increase in uninsured rates between 1998 and 2003.

-- By Lea Winerman, Online NewsHour