The contract was awarded to consultants Hall & Partners Open Mind, whose website says it specialises in brand and communications research with "fresh new approaches to measuring consumer engagement and participation with brands".

A Senate hearing was told last week that Hall & Partners had conducted 30 focus groups on the report since November.

"That has been through a couple of different stages of the research and has obviously been conducted across a number of groups in various locations, various demographics," the head of treasury's ministerial and communications division Luke Hickey told the committee.

Asked about the content of Thursday's report in Parliament, Treasurer Joe Hockey refused to say whether the immigration numbers in it had been adjusted by the government after being prepared by the Department of Immigration.

He said merely that the immigration numbers in it would be larger than Labor's.

Labor has accused the government of picking low estimates for population growth in order to maximise the apparent gulf between the size of the future workforce and the number of retirees it must support. Such an adjustment would also force up the size of the projected budget deficit.

Mr Hockey told a NSW business chamber breakfast last week that "when people see some of the graphs in the Intergenerational Report they are going to fall off their chairs."

"For all the effort we've put in so far, and some of it has been controversial, for all the effort we've put in so far, we still don't get anywhere near being able to reduce spending over the medium-term to the same level that exists today as a percentage of GDP," he said.

The Intergenerational Report is required by law every five years. It assesses the long-term sustainability of the government's policies 40 years into the future. Finance Minister Mathias Cormann told the Senate hearing the wording of the report was the responsibility of the government and not the Treasury.

"We rely on the best advice from high-quality public servants in Treasury but, ultimately, the government is responsible for what is put forward and the government will justify and explain the implications and engage in the conversation about what courses of action we need to pursue as a country to put ourselves on a stronger foundation for the future," he said.

The first Intergenerational Report in 2002 predicted that the ageing of the population and extra spending on health would help push up the budget deficit around 5 per cent of gross domestic product. The figure was revised down to less than 3 per cent in the second report and to less than 2 per cent in the third on the back of faster than expected population and employment growth.

Demographers have already warned the government's Intergenerational Report may project Australia's population will hit close to 38 million by 2050, relying on an assumption of net overseas migration of 240,000 people a year.

That could re-open debate about a "Big Australia" because it is a larger projected population than was found in the previous report, which projected a population of 35 million by 2050.

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