The Labour Party is questioning the value of a $1 million study of what beneficiaries cost the state over their potential working life.
The Government-commissioned report studied those on invalid, sickness, unemployment and domestic purposes benefits over a two-year period and calculated that their cost to the taxpayer, until they reached 65, would be $78.1 billion.
The valuation uses a baseline of anyone receiving welfare benefits in the 2010-2011 year and applies averaged data from the past 20 years of the likelihood of them staying on benefits, moving off them or going between benefits.
Labour's social development spokesperson Jacinda Ardern says much of the information was available 18 months ago and common sense tells the rest of the story.
But the Government says the data will help it decide where to invest earlier to get people off welfare.