A possible explanation

But, adds Orme, the income difference can be linked, at least in part, to a cultural and social diversity that's unheard-of in most other nations.

"It's not surprising -- we are a hugely diverse country," he says. "Compare suburban Boston with a county on the Texas-Mexican border. You simply don't find those extremes in other industrialized countries."

So that raises the question: At what income level does the average American begin to feel the financial noose loosen just a bit? Naturally, every little bit helps, but Hill suggests it takes a good deal more income for someone to feel on the cusp of financial security.

"It's not until about $50,000 where people reach the place where they don't need any help, and it's not until the $60,000 to $70,000 range that they begin to stop living beyond their means," he says. "They would certainly be getting by, but they wouldn't be doing great. Realistically, you would almost need to double that income average in the United States to feel like you were living a reasonable life."

Another worry for Americans

Further sharpening many Americans' struggles is the all-too-common absence of health insurance (estimates put the range of uninsured between 45 million and 48 million, or 14% to 15% of the population).

While most other countries that placed high on the U.N. Human Development Report have lower median incomes than the United States (including Australia, the Netherlands and Ireland), the guarantee of health care removes the anxiety of a costly illness.

Along those lines, the Corporation for Enterprise Development, a Washington, D.C., advocacy group, estimated in late January that 43% of U.S. households -- roughly 127 million people -- would fall below the poverty line within three months if confronted by a serious medical illness or some other emergency.

"In a lot of countries where the social safety net is much larger, such as Sweden and Canada, nobody has to worry about health care," Hill says. "In the United States, a person making that median income likely doesn't have health insurance. If they do, they are fortunate among their friends who probably don't have coverage."

But the news is not entirely negative. For one thing, although the level of financial disparity in the U.S. is high compared with its Western peers, it's far from the worst in other parts of the world. For instance, the spread between the haves and have-nots in countries such as Chile and Brazil is much greater -- and even more so in countries in Africa, the Caribbean and other regions where relatively few, exceedingly wealthy people live with an enormous population existing in crippling poverty.

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And if you happen to be one of the fortunate Americans who count themselves as relatively well off, it doesn't come with the grim circumstances that often exist in other countries where income disparity is more than a matter of numbers.

"Wealthy people have access to things that ordinary people don't have. But they're not happier than others -- there's simply no data to suggest that," Hill says. "And you're also a big target to others who resent your wealth. That means kidnappings and other crimes. You almost have to live like a drug lord in some of these places because you stand out so much. You're much more powerful, but you also face a certain amount of isolation."