Many optimists on US growth base their upbeat projections on hopes that inventories are reaching a low. Even a slow down in the rate of inventory drawdown can produce a rise in GDP.

This argument underpins a highly bullish forecast published by Brian Westbury and Robert Stein of the First Trust Advisors in Wheaton.

They believe that this will add significantly to growth in the second half of the year.

But this can make the economy look more robust than it actually is. Final sales are in some ways a better overall determinant of economic health.