MARRIAGE, and its many ups and downs, still exercises a powerful hold over newspapers, magazines and the airwaves. Nearly 23m Americans watched Prince William being joined in holy matrimony to Kate Middleton. Millions more have wallowed in the break-up of Arnold Schwarzenegger's marriage after revelations that he fathered a son with a maid. And the tumescent tweets of congressman Anthony Weiner have stirred up endless speculation about the health of his own year-old marriage and the forbearance of his newly pregnant wife.

Less titillating are revelations about the sorry state of marriage across the United States. Data from the Census Bureau show that married couples, for the first time, now make up less than half (45%) of all households.

The iconic American family, with mom, dad and kids under one roof, is fading. In every state the numbers of unmarried couples, childless households and single-person households are growing faster than those comprised of married people with children, finds the 2010 census. The latter accounted for 43% of households in 1950; they now account for just 20%. And the trend has a potent class dimension. Traditional marriage has evolved from a near-universal rite to a luxury for the educated and affluent.

There barely was a marriage gap in 1960: only four percentage points separated the wedded ways of college and high-school graduates (76% versus 72%). The gap has since widened to 16 percentage points, according to the Pew Research Centre. A Census Bureau analysis released this spring found that brides are significantly more likely to have a college degree than they were in the mid-1990s.

“Marriage has become much more selective, and that's why the divorce rate has come down,” said Bradford Wilcox, director of the National Marriage Project at the University of Virginia in Charlottesville. The project found that divorce rates for couples with college degrees are only a third as high as for those with a high-school degree.

Americans with a high-school degree or less (who account for 58% of the population) tell researchers they would like to marry, but do not believe they can afford it. Instead, they raise children out of wedlock. Only 6% of children born to college-educated mothers were born outside marriage, according to the National Marriage Project. That compares with 44% of babies born to mothers whose education ended with high school.

“Less marriage means less income and more poverty,” reckons Isabel Sawhill, a senior fellow at the Brookings Institution. She and other researchers have linked as much as half of the income inequality in America to changes in family composition: single-parent families (mostly those with a high-school degree or less) are getting poorer while married couples (with educations and dual incomes) are increasingly well-off. “This is a striking gap that is not well understood by the public,” she says.

Do not expect the Democratic Party, however, to make an issue of the marriage gap in next year's elections. Unmarried women voted overwhelmingly for Barack Obama. “You don't want to suggest to someone who isn't married and has children that they should be married,” says Ms Sawhill. “That is a denigration of their lifestyle.”