An Opposition party wants the Government's public sector results independently audited.
NZ First says ministers tout falling benefit numbers as an indication people are finding work, but that's not always the case.
"We can't assume that falling benefit numbers are a good thing when as many as two out of five people coming off benefits are not going into work or study," says social development spokesman Darroch Ball.
"Until the Government agrees to independently audit its public service target results, they are only masking reality and making it look as though they're achieving something they're not."
He's citing figures issued by the Council of Trade Unions, obtained from the Ministry of Social Development under the Official Information Act.
CTU economist Bill Rosenberg says they show that in 2014 only 46 percent of people who came off a benefit obtained work.
"Even adding on the 11 percent going into full-time study, that means as many as two out of five people leaving benefits aren't going into work or study," he said.
"The information also shows the ministry has no way or knowing what quality of work they find - do they get zero hour, casual or low paid work, or go onto 90-day trials?"
Mr Rosenberg says the approach which assumes getting people off benefits is always good should be treated cautiously.
"It isn't always good, particularly if people don't find good quality jobs."