People may move up or down the social ladder within their lifetime or from one generation to the next. That everyone has the same chance of moving up is what lies behind the idea of equality of opportunity.

One way to measure social mobility is to see whether rich parents have rich children and poor parents poor children, or whether the incomes of parents and their children are unrelated. Can children of poor parents become rich? Researchers at the London School of Economics have used this method to compare social mobility in eight countries. Using their data, we have shown that, at least among these few countries, the more equal countries have higher social mobility. It looks as if the American Dream is far more likely to remain a dream for Americans than it is for people living in Scandinavian countries. Greater inequalities of outcome seem to make it easier for rich parents to pass on their advantages. While income differences have widened in Britain and the USA, social mobility has slowed. Bigger income differences may make it harder to achieve equality of opportunity because they increase social class differentiation and perhaps prejudice.