Revisions

By THIS IS MONEY
Updated: 04:59 EST, 31 March 2010

The Daily Mail's City team explain the changes the Office for National Statistics makes to it's figures and how they made a horrible GDP reading somewhat more credible...

GDP looked better after ONS revisions

Exam time again?

Nope, nothing to do with ALevels or GCSEs.

These are changes to official figures made by the government's bean counters.

Important?

Yes. The Office for National Statistics' first stab at a piece of data is often based on partial evidence.

So as further information comes to light, the ONS's number crunchers in Wales will get out their calculators and have another crack.

The changes can be so large that the Bank of England generates its own estimates of what it thinks the final estimate of GDP will eventually show.

For example?

Well, take yesterday's Gross Domestic Product figure for the fourth quarter.

The first tilt at this had growth at a paltry 0.1%, which was widely seen as a bit of a humiliation for Gordon Brown. But this was subsequently revised up to 0.3% and then 0.4% yesterday - a far more creditable number.

Are they common?

Much of the ONS's data is subject to revision, but not all of it.

For example, statisticians tend to get the inflation data right the very first time, meaning they leave old figures untouched.

That makes the Consumer Prices Index one of the government's more reliable indicators.