Excellent work by Jonathan Jones putting together an analysis of how right (or rather, how wrong) the initial quarterly GDP estimates are:
Whatever figure the ONS tells us GDP grew by in the third quarter of 2012, there’s one thing you can be pretty sure of: it won’t be the actual amount GDP grew by in Q3. In the past 51 years, just 12 of the ONS’s 205 first stabs at quarterly growth have survived later revisions…
It’s not unheard of for the initial estimates to be out by more than three points. In June 1971, for example, the ONS estimated that GDP had fallen by 4.5 per cent in the first quarter of the year — by far the worst drop in any three-month period. The ONS now says that GDP fell by just 0.9 per cent — bad, certainly, but nowhere near as terrible. Or take 1988 Q3: the first estimate of –2.3 per cent has since been revised to +1.4 per cent.
But there is an ONS success story here too. As the top graph shows, preliminary estimates have become a lot more accurate. There hasn’t been a miss of more than 1.3 points since 1988. And in the last 20 years, the average revision has been 0.4 points compared to the one-point average in the previous 30 years.