WHEN JIMMY Carter, the Democratic candidate for American president in 1976, desired to criticise the file of the incumbent Gerald Ford, he reached for a number invented by the economist Arthur Okun. A tough-and-ready indicator of the issue of the economy, what Okun known as the financial discomfort index added together the unemployment rate with the stage of inflation. Four years later Ronald Reagan, the Republican candidate, renamed the indicator to the pithier misfortune index and used it against Mr Carter, who had presided over rising inflation and unemployment. Reagan went on to fetch the election and the following one, in 1984, because the index fell on his gape.