The statistic sits out there on the health care landscape like a beached whale: 43 million Americans have no medical coverage. But the statistic is so huge and amorphous--in the distance--that it has yet to prompt much compassion, let alone action.

Who exactly are the uninsured?

Most are poor working Americans who don't get offered insurance with their jobs and aren't eligible for government programs.

But the face hit hardest by the nation's coverage crunch is that of the single woman. Working-age women who are separated, divorced, never married or widowed are most likely to have no health insurance, most likely not to get needed care.

That is a finding from the recent comprehensive survey of women's health by the Commonwealth Fund. About a third of all single women under age 65 in the survey had health insurance problems. They were either uninsured or went without coverage at some time during the past year.

"That's an extraordinarily high number," says economist Cathy Schoen, vice president for research and evaluation at the Commonwealth Fund.

It's extraordinary, too, because, with a rolling economy and tight job market, you'd expect the rates of uninsured to go down--for both women and men. "What is surprising and disturbing," continues Schoen, "is that these statistics are showing up when we have one of the best economies in 30 years. We're losing ground despite a good economy."

There are several reasons why single women are especially at risk. To begin with, just being married is a financial advantage because it gives you a double shot at getting health coverage from an employer--and being able to afford the premiums if both spouses are working. In the survey, conducted in 1998 by Louis Harris and Associates Inc., 32 percent of single women had health insurance problems compared with 23 percent of married women.

But the most significant factor is income. The dividing line for health coverage comes at an annual income of about $35,000. Regardless of marital status, women in families earning less than that amount are at high risk of being uninsured. The lower the income, the higher the risk. For example, nearly half of women with family incomes of $16,000 or less went without coverage, while 90 percent of married women with family incomes above $35,000 had health insurance.

At the same time, single women are much more likely to fall on the wrong side of the economic dividing line. In the survey, while 60 percent of married women had annual family incomes above $35,000, nearly 70 percent of single women earned less than that amount. What's more, women tend to cluster in jobs that don't offer coverage or don't help pay for the premiums. An individual policy costs about $2,000 a year; a policy that includes children, about $5,000. "If you're a middle- or low-income worker, you're unable to pay for it yourself," says Schoen.

The older woman who is separated or divorced in midlife may be especially hard hit. "For years she's been insured on her husband's policy. Now she is losing the coverage she's always had and coming in new to the work force," says Schoen. "Men are much less likely to be dependent on their wife's policy. Getting a divorce in the middle years, they are less likely to lose their health insurance."

To be sure, single men are also at a similar high risk of not having insurance. The difference is that not having coverage poses a greater medical burden for women. That's because women need more medical services than men, not only for themselves but for their families. Single women, for example, are much more likely to have dependent children than single men.

Biology also prompts women to use more medical services than men, especially at younger ages. Pregnancy, for example, is a major medical expense, and all women starting in their teenage years are encouraged to have regular preventive care with Pap smears and breast exams. Men are relatively healthy in their young adult years, Schoen points out. They don't have to get preventive tests such as prostate exams until they are about 50.

All this adds up to a bigger problem for women in getting care. The Commonwealth Fund survey, which included 2,850 women and 1,500 men, asked if there had been a time in the past year when people needed medical care and did not get it. For example, the survey asked, did you not see a specialist when you needed to? Did you not get a prescription filled because of the expense?

Nearly half of uninsured single women reported a problem with getting medical care, compared with about a third of uninsured single men. In other words, the researchers concluded, uninsured single women are at 40 percent higher risk than uninsured single men of not getting needed medical care.

So the next time you try to grasp the problem of the uninsured, you might start by imagining the face of a single woman.