Explaining : The three estimates of Gross Domestic Product.
Pete, explain why there are three releases each quarter.
Mainly because more data becomes available. We can estimate GDP in any one of three ways in production, income and expenditure. They are all theoretically equal but they all have different data sources. Some are monthly, some are quarterly and some are annually.
On the output side we have a lot of data available rapidly, from monthly business surveys and that enables us to produce an output based estimate of GDP after approximately twenty-five days. Which is one of the fastest in the world. But we don’t publish a lot of detail at that stage.
About a month later we publish the second estimate which has more detail on the output side but also some aggregated expenditure and income data.
Four weeks after that we publish the Quarterly National Accounts which has more detail on all three approaches and also includes the quarterly Sector Accounts.
And why do we revise GDP ?
OK. There are simple reasons, the simplest of which is that we get more data. We publish our best estimate at any given moment in time and as more returns become available and new surveys come on stream, which can mean the picture will change.
Initially the more data you get in can affect seasonally adjustments and can cause revisions. We have an annual balancing process which we have in our annual Blue Book publication and that causes significant revision to recent years.
And finally we can change the classifications; the legal framework and the concepts and the definitions. They change from time to time and these can cause revisions all the way back in the series.