A retirement policy expert has rejected a report by the ANZ that claims KiwiSaver may not be reaching the people who most need help with saving for their retirement.

The bank, which is also the country's largest KiwiSaver provider, released a raft of recommendations on Tuesday as part of an assessment of the scheme, which turned 10 years old on July 1.

The research found that although 80 per cent of those surveyed who earn more than $100,000 were members, just 53 per cent of those who earned less than $50,000 had signed up.

But Michael Littlewood, who was previously the co-director of the Retirement Policy and Research Centre at Auckland University, said it was no surprise to see lower KiwiSaver membership for those on lower pay - but it did not mean they should join the scheme.

"Of course we should expect the lower-paid to have lower levels of KiwiSaver membership.

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"However, it's another step to say they should be members because that assumes they aren't saving enough for retirement."

"We cannot know the answer to that without a full needs analysis at a household level with full asset/liability measurement."

Littlewood said some people could not afford to join KiwiSaver or would see a cut of 6 per cent in their take-home pay if they joined because some employers used a total remuneration policy.

He pointed to Reserve Bank figures that showed KiwiSaver represented 5.3 per cent of all households' financial assets last year and 2.5 per cent of all assets.

"We really cannot tell anything about households' preparedness for retirement by looking at just KiwiSaver memberships."

Littlewood also questioned whether the public would be keen to make the scheme compulsory if they were told that doing so would reduce their take-home pay or be used to means test how much New Zealand superannuation they got.

The ANZ research found 60 per cent of those surveyed would like to see membership of the scheme made compulsory and 33 per cent were opposed the idea.

Littlewood said before the 1997 referendum on whether New Zealand should introduce a compulsory superannuation saving scheme, polls showed 68 per cent initially favoured compulsion.

But he said, once the public knew that it would effectively mean an 8 per cent cut to take-home pay the support halved.

"Then, when we discovered that 'National Superannuation' would be reduced by the value of compulsory retirement savings scheme benefits, support for compulsion evaporated."

"The latest 60 per cent result was probably obtained from survey participants in the absence of any indication of what a compulsory KiwiSaver scheme would actually mean for the public."

Littlewood said New Zealand needed to undertake a longitudinal survey to better understand people's financial behaviour.

"Asking people what they think is pointless."