(Image: AP/J. Scott Applewhite)

You likely heard of the frightening unemployment number from the US on Friday their time: the unemployment rate rose to 14.7%, with 20.5 million jobs lost in April. Just two months ago, the unemployment rate was 3.5%, a 50-year low. The rise means the jobless rate is now worse than at any time since the Great Depression.

Except, it was worse. Much worse. And not just in an obscure way that's only of interest to labour economists.

There was a mistake in the classification of some of the jobless, which meant the unemployment rate should have been 19.5% instead of 14.7%. The US Labor Department revealed in a note to the figures that its survey-takers erroneously classified millions of Americans as employed in April even though their employers had closed down.