As previously noted on the Deep End, neither Britain nor America has any right to call itself a land of opportunity. International comparisons place the two countries at the bottom of the league for social mobility and at the top for inequality.

Many progressives, including the President of the United States, believe that these phenomena are closely related:

“Economic inequality is the ‘defining challenge of our time,’ President Barack Obama declared in a speech last month to the Center for American Progress. Inequality is dangerous, he argued, not merely because it’s unseemly to have a large gap between the rich and the poor, but because inequality, itself, destroys upward mobility, making it harder for the poor to escape from poverty. ‘Increased inequality and decreasing mobility pose a fundamental threat to the American Dream,’ he said.

In an article for the Atlantic, Bradford Wilcox summarises the underlying theory:

“Princeton economist Alan Krueger, and economist Miles Corak… have all argued that it’s harder for the poor to climb the economic ladder today because the rungs in that ladder have grown farther apart. In Krueger’s words, countries like the United States with high inequality tend to have less upward mobility ‘for children from low-income families.’”

This would seem to make sense, but evidence has emerged that suggests that inequality is not the main obstacle to social mobility. The data-set in question allows us to look at the significant differences in social mobility between different communities within America:

“So what factors, at the community level, do predict if poor children will move up the economic ladder as adults? What explains, for instance, why the Salt Lake City metro area is one of the 100 largest metropolitan areas most likely to lift the fortunes of the poor and the Atlanta metro area is one of the least likely?”

Statistical analysis shows that three factors are of particular importance in predicting the likelihood of upward social mobility:

“Per-capita income growth… Prevalence of single mothers (where correlation is strong, but negative)… Per-capita local government spending

“In other words, communities with high levels of per-capita income growth, high percentages of two-parent families, and high local government spending—which may be a proxy for good schools—are the most likely to help poor children…”

What’s interesting about these three factors is their lack of an obvious link to inequality:

“But many measures directly related to income inequality—such as the size of the middle class in a community, or the gap between the richest and poorest middle-class households in communities—seem far less important [in predicting social mobility] than local growth, two-parent households, and local spending.”

Further research is required – for instance, in determining the direction of causality and in establishing whether the same relationships apply to other countries. But if the same factors do apply to Britain, what would the policy implications be?

Per capita local spending is more even in Britain than America, so that seems unlikely to be a particularly relevant issue for us (though the effectiveness of such spending – especially on schools – almost certainly is). As for maximising per capita income growth, that already is a widely shared policy objective.

So, that leaves the issue of family structure and, therefore, marriage. Here, despite the accumulating evidence that family stability is of enormous importance in supporting all kinds of beneficial social outcomes, most of our politicians refuse to engage with the issue.

In particular, Nick Clegg is relentlessly hostile to any pro-marriage move on the part of the Coalition. Just as well then that he’s not responsible for the Government’s social mobility agenda… oh.