The Institute for Fiscal Studies (IFS) said the Government's figures on take home pay do not reflect what has happened to household incomes overall.
IFS director Paul Johnson told BBC Radio 4's Today programme that although the Government used "a perfectly sensible set of numbers", there were "two problems" that need to be taken into account.
He said: "First, we have other sets of data - the Office for National Statistics publishes an average weekly earnings index. That went up quite a lot less quickly than inflation in the most recent months.
"And of course they are not taking account of reductions in things like benefits which were occurring over the time. So if you are looking at household incomes, that will be different from what's happened to take home pay."
Labour leader Ed Miliband said David Cameron has "shown millions of people he doesn't understand their lives" after the Prime Minister claimed there are "positive signs" that take home pay is rising:
All the PM does by telling Britain there isn't a cost of living crisis is show millions of people he doesn't understand their lives
Cathy Jamieson MP, Labour’s shadow treasury minister, said the Coalition's claim that take home pay was rising was based on "highlyselective figures".
The Tories are totally out of touch to claim people facing a cost-of-living crisis are actually better off under them.
These highly selective figures from the Tories do not even include the impact of things like cuts to tax credits and child benefit which have hit working families hard.
The truth is that under David Cameron real wages have fallen by over £1,600 a year and analysis of IFS figures show families are on average £891 worse off as a result of tax and benefit changes since 2010.
At the same time this government has given a huge tax cut to people earning over £150,000.
The Prime Minister has insisted there are "positive signs" that take-home pay is rising.
An analysis of take home pay figures circulated by the Treasury has suggested all but the top 10% of earners saw a rise last year.
Overall people saw their take home pay rise by a third more than the rate of CPI inflation, currently 2%.
The Chief Secretary to the Treasury Danny Alexander has defended the Government's plan to allow councils which give fracking the go-ahead to keep 100 per cent of the business rates they collect.
Asked if that amounted to a bribe, he told ITV News: "Fracking offers a significant opportunity for the UK economy. It's a potential source of considerable amounts of energy for our country.
"In common with other areas of energy development where local authorities are allowed to keep business rates, and where there are other incentives for communities - it's important and fair we should treat fracking in the same way."
The Treasury has pledged to honour all UK Government debt up to the date of potential Scottish independence, if Scots vote in favour in September's referendum.
ITV News Business Editor Laura Kuenssberg explains:
And important #indyref story - Treasury will stand behind all UK debt - move to prevent market jitters about Scotland going it alone
The Polish prime minister has criticised David Cameron for singling out Poland in his vow to ban British child benefit payments to children of EU migrants.
According to Treasury figures, over half the children in EU nations who receive child benefit are in Poland.
According to Treasury figures - the UK pays child benefit to 40,000 children living in another EU member state.
More child benefit figures: govt pays it to 13m children of which 40,171 live in EU (Poland 25,659, RoI 2,609, France 2,003, Slovakia 1,881)
The Treasury has confirmed that the government will announce budget cuts of 1% to departments over the next two years.
Making the announcement on Twitter the Treasury said:
Resource budgets in government departments cut by around 1.1% over next two years #responsiblerecovery
No cuts to capital, health, schools, aid, HMRC, local gov & security services. MoD given exceptional flexibility #responsiblerecovery
In another message the Treasury said: "Chancellor & Chief Sec have written to cabinet to inform them an extra £1bn a year savings will be made over next 3yrs."
The Treasury has claimed an independent Scotland could cost Scottish taxpayers £1,000 a year.
The Chief Secretary to the Treasury Danny Alexander said the calculation was based on the "most optimistic independent assessment of Scotland's finances" by the Institute of Fiscal Studies think tank, which published its report last week.
In a letter to Scotland's First Minister Alex Salmond, Mr Alexander cited the IFS' statement that independence would require policy action "equivalent to around an eight percentage point increase in the basic rate of tax".
He said Treasury officials calculated this would mean an average increase for basic rate tax payers in Scotland of around £1,000 per year.