Incapacity benefit test claims 'conflated figures' - watchdog
Suggestions that 878,300 benefit claimants dropped their claims rather than take a medical test have been challenged by the statistics watchdog.
Tory chairman Grant Shapps was quoted saying that nearly a million people had "taken themselves off" incapacity benefit instead of sitting the test.
But the UK Statistics Authority has said that figure appears to "conflate" new and old claims.
Labour said the Tories were "misusing statistics for their own ends".
Employment and Support Allowance replaced incapacity benefit for all new claimants who are unable to work due to incapacity or illness.
'Taken themselves off'
Tests have been going on since 2008 to assess whether new claimants are entitled to ESA, and existing incapacity benefit claimants have been reassessed since 2011.
The figures, widely reported in March, suggested 878,300 people who were already claiming incapacity benefit had decided not to take the tests and dropped the claim instead.
Mr Shapps - party chairman and minister without portfolio - was quoted as saying: "This is a new figure, nearly a million people have come off incapacity benefit... before going for the test. They've taken themselves off. My big argument here is this is not these people were trying to play the system, as much as these people were forced into a system that played them."
But the chairman of the UKSA, Andrew Dilnot, said in a letter to Labour MP Sheila Gilmore: "Having reviewed the article and the relevant figures, we have concluded that these statements appear to conflate official statistics relating to new claimants of the ESA with official statistics on recipients of the incapacity benefit who are being migrated across to the ESA".
He points out that of 603,600 people already on incapacity benefit who were reassessed between March 2011 and May 2012 - 19,700 claims were closed before they underwent the tests.
The higher figure of 878,300 appeared to relate to the total number of claims closed by new applicants for ESA between October 2008 and May 2012, he said.
Mr Dilnot said that research by the Department for Work and Pensions suggested that one important reason for those cases being closed was because the person "recovered and either returned to work or claimed a benefit more appropriate to their situation" instead.
Shadow work and pensions secretary Liam Byrne said: "This is a government that doesn't like to let the facts get in the way of a good story... but it really is outrageous that the Tories have been caught yet again misusing statistics for their own ends."
Work and Pensions Secretary Iain Duncan Smith's figures were criticised by the statistics watchdog earlier this month over claims about his benefit cap.
A Conservative spokesman said the government was "fixing the welfare system to make work pay".
"We're capping benefits so that no out-of-work household can claim more than the average working family earns and introducing universal credit so it always pays to work.
"The same old Labour Party have opposed every single measure we've taken to fix welfare."
In a report published on Wednesday, the Commons public administration select committee said government statistics must be presented in a fair and accurate manner - "unspun" - to underpin good policy making.
It urges press officers to work with statisticians "much more closely to ensure that press releases give an accurate and meaningful picture". But the report also calls on the statistics watchdog to explain why it chooses to intervene publicly on some issues and not others.