DO YOU remember the double-dip recession of 2012? It’s a collector’s item. Two years into a slow climb from the nadir of the 2008-2009 slump, Britain’s Office for National Statistics (ONS) announced that the UK’s economy had shrunk by 0.2 per cent in the last quarter of 2011, and the same again in the first three months of 2012. But then it changed its mind.

By mid-2013, the ONS had taken another look at the data and decided that output had been flat during the first quarter of 2012: recession retracted. The revisions continued and as of today, the ONS’ best estimate is that Britain’s economy grew by 0.8 per cent in Q1 2012 – a full percentage point upgrade in all.

If it sounds like I’m being critical, it shouldn’t. Measuring gross domestic product (GDP) is extremely complicated. Around the world, national statistics offices are struggling to get the sums right the first time around.