New Zealand is virtually the only country to have raised the age at which people receive the retirement pension - from 60 to 65, over the 1990s - and Disney has studied the impact of that shift.

The change saw a rise in participation in the workforce by older people - not only those in the 60-64 group but most noticeably the group in their 50s.

"They are now looking at their wealth. They might choose to retire at 57 if they have enough. Or they might choose to retire at 67. So deciding when to retire can affect people’s behaviour over a decade."

Governments may increasingly give people the option of taking their pension at a later date, and actuarially adjusting their entitlement accordingly, he says.

That will not only help the government with its finances, but will also provide a boost to the productive capacity of the economy by keeping people in the workforce longer.

Disney’s research on the impact New Zealand’s raising of the retirement age is that it increased participation in the economy and probably increased economic growth as a result. He compared New Zealand workplace participation rates by age with those of Australia over the period.

"If you assume economic conditions remained the same, the participation rates of New Zealanders aged 55-59 went up by 14%. Now co-relation is not causation - there were other factors I am sure - but Australian participation for the same group went down by 6%.

"I’m not sure I completely believe the extent of that statistic, but it does tell us that the change in the age people get the retirement pension is a forward looking thing, and it has an impact on the decision. And I would say the reform has had quite a strong effect on the economy."