In recent months there have been a few changes to KiwiSaver with more under consideration.

But those who are inclined to tinker with the scheme should be looking at the evidence on its efficacy and thinking about whether any changes are consistent with its objective – to help those with a savings problem save more for their retirement.

You may have missed it, but the Government will now be ensuring that savings in default KiwiSaver funds are invested ‘more responsibly’. That’s a worry, especially given that so called ethical investment choices already exist in the market.

For now, investing ‘more responsibly’ means excluding any investments in fossil fuel production and reflects the Government's commitment to its climate goals.

But addressing the impact of climate change is not the objective of KiwiSaver. Pursuing multiple objectives in this way makes it less likely that KiwiSaver can actually do what it was intended. It also misses the fact that we have a much better policy to address climate change – the Emissions Trading Scheme.

Beyond this, where will the Government’s prescription for ‘responsible’ investment end and what will it cost us? Will we next be required to invest in local infrastructure or electric vehicle production and be prohibited from owning shares in companies that manufacture utes or barbeques?

The Government is also investigating a proposal to increase KiwiSaver contributions. New members, and those who opt into it, would see their contributions increase from 3 to 10 per cent.

This is surprising because KiwiSaver has been rigorously evaluated against its objectives and was found to be a poor performer. Good public policy scales back failures it doesn’t scale them up.

I worked on that evaluation for several years, undertaking two major studies. To summarise: KiwiSaver membership had no effect on net wealth accumulation, and it was highly inefficient and wasteful. On top of that it doesn’t even boost savings at a national level.

Over the last decade, despite their complaints, KiwiSaver proponents have been unable to provide any rigorous evidence showing the scheme has been successful at meeting its objectives.

In the meantime, the international evidence base on the efficacy of schemes like KiwiSaver keeps growing. It turns out our experience is not unique. For instance, Harvard Professor Raj Chetty and his co-authors examined 41 million observations on savings for the population of Denmark and found that each additional dollar of government expenditure on subsidies increased total saving by only one cent.

It would be great to see more attention paid to evidence in public policy decision making.