GDP figures overstate the national income available to Irish people to spend. Ireland's diplomats in Brussels wised up to this long ago. When they want to crow about the brilliant economic policies that created the Celtic Tiger, they use the GDP figures, noting proudly that Irish GDP per person is now the third-highest in the EU, well above Britain's. However, when the talk turns to EU regional subsidies, the diplomats switch to the “more appropriate” GNP measure, which puts Ireland close to the EU average, and mutter about the country's huge infrastructure backlog.

As the Irish economy develops, GDP and GNP might be expected to converge, but instead the gap seems to have widened recently. That is largely because American multinationals have been racking up (or at least recording) such big profits in Ireland. In some ways, this is a mark of the country's economic immaturity, and its failure to nurture indigenous industry. Chris Coughlan, a vice-president of HP Compaq and chairman of the Galway Chamber of Commerce, suggests that Ireland's future success could be measured in part by whether GDP and GNP converge, which would indicate that home-grown industry has matured. That might, sadly, put an end to another splendid quirk with which to confuse those first-year students: that Ireland's total exports exceed the country's national income.