Error and fraud statistics are based on the Error and Fraud Analytical Programme - an annual statistical enquiry run by HMRC designed to measure levels of error and fraud in finalised tax credit awards.
Further details of HMRC's measures to tackle error and fraud were published on 14 July 2008 in the document Reducing error and fraud in Tax Credits.
Each set of Error and Fraud Statistics are based on the results of the Error and Fraud Analytical Programme as at the May a year after the end of the tax year that the awards relate to, even at this point occasionally not all cases have been completed.
A revised set of estimates are produced the following year, alongside the next years report, and if the central estimate for the error and fraud favouring the claimant has changed by more then 0.2 percentage points then a revised publication will be published.