Managing interest rate expectations is one of the most difficult tasks for any central bank governor. If expectations prove out of kilter with your own, there is a risk of market disruption. This can also complicate the conduct of monetary policy itself. So far Ben Bernanke, who took over from Alan Greenspan as chairman of the US Federal Reserve in February, has faced few communications difficulties. Having inherited a clear - and widely understood - phase of interest rate tightening that began in June 2004, Mr Bernanke duly raised rates in March and is expected to do so again next week (in what would be the Fed's 16th consecutive quarter-point increase).

After that, however, America's interest rate outlook starts to look a little foggier. In his testimony to Congress this week, Mr Bernanke said that robust consumer spending and strong housing sales in March had not "materially changed" the Fed's view that US growth would begin to decline later this year to the economy's trend rate of between 3 and 3.5 per cent. Yesterday's data, showing a strong 4.8 per cent expansion in US gross domestic product in the first quarter of 2006, had been anticipated as a rebound following the sharp fall in activity brought about by Hurricanes Katrina and Rita last year.