OPINION: Comedian Bill Maher has a great bit on his HBO show where he proposes a new rule at by which people should govern their lives. The point is usually to expose the absurd hypocrisy of political behaviour or thinking.

On the topic of immigration, Maher said "New Rule: You can't spend the first half of a debate bitching about how immigrants are ruining the country, and the second half telling uplifting stories of your immigrant parents."

It is time we applied it to the immigration debate in New Zealand. Too often it seems that we, as a society, are happy to celebrate what a great country New Zealand is while simultaneously moaning that immigrants are ruining it for everyone.

MURRAY WILSON/FAIRFAX NZ New Zealand First leader Winston Peters has been the most notable of Kiwi politicians making fact-free assertions about immigration, argues Jason Krupp.

The evidence of this can be seen in the public discourse. Various migrants have been blamed for pushing up house prices, eroding wage increases, importing radical ideologies, and diluting what it means to be a Kiwi.

READ MORE:

* Nigel Latta: the truth about immigration

* The Government's slow awakening on immigration

* Immigration tipping point - are we there yet?

* Shamubeel Eaqub: Immigration an emotionally charged topic

There is, of course, nothing wrong with raising these concerns, provided it is accompanied by an effort to tell whether there is a factual basis to support these fears.

Unfortunately, this does not seem to be the case when it comes to politics, where fact-based arguments have been thin on the ground of late. Almost all the opposition parties are guilty of this to some extent, but none more notable than New Zealand First and party leader Winston Peters.

This is a significant concern. Voters will head to the ballot box later this year, and the choices they make will have far reaching consequences for good or for ill. We at The New Zealand Initiative believe that informed voters make better decisions. That is why my colleague Rachel Hodder and I spent the last six months researching immigration in detail.

Our report, The New New Zealanders: Why Migrants Make Good Kiwis, covers both local and international academic research and our own analysis of the General Social Survey and the Election Survey, and aims to paint a factual picture of immigration in New Zealand.

Broadly, we found that many of the concerns about immigrants diluting Kiwi culture did not hold up in the data. Immigrants of all stripes tended to integrate well into New Zealand. Not only did they claim welfare and other benefits at a lower rate than native born New Zealanders, they also had good employment outcomes, and educated their children to a very high level.

Our research also found very little evidence of ethnic clustering, and we found that over time the views and labour market attributes of immigrants converged towards the New Zealand average. In other words, immigrants might come here as foreigners, but they become Kiwis in the long run (hence the title).

Furthermore, many of the economic fears that people have about high levels of immigration proved to have little substance.

Work by two of New Zealand's most respected economists, Jacques Poot and Bill Cochrane, showed that Kiwis are likely to have a more profound effect on house prices than immigrants. That's because most immigrants are here on a temporary basis, and so are unlikely to be in a position to buy a house. Instead, it is returning Kiwis and those who have chosen to stay in New Zealand due to our relative economic outperformance that are pushing up prices in the housing market.

Of course, we recognise that migrants compete with Kiwis in the rental market. But cutting off immigration is going to do little to tackle the logjam that prevents houses from being built in the first place. That fault lies with the regulations the Parliament imposed on New Zealand.

There is also little evidence of immigrants stealing jobs from native born New Zealanders. Were this the case, it would most likely be seen at the low-skill end of the labour market, and yet demand for labour in this area is growing strongly according to recent job ad numbers.

We acknowledge there are costs associated with immigration for which we do not have all the answers. The effect on Maori, and the position of New Zealand's first inhabitants in an increasingly diverse society is one. The other is infrastructure. But we think that the focus should be on finding ways to address these concerns without sacrificing the benefits of immigration.

We accept that not everyone will agree with our analysis, and many will challenge us on the conclusions we have drawn in the report. Indeed, we welcome this kind of discourse. It is how good ideas are tested and bad ones eliminated.

What is unwelcome is fact-free rebuttals.

Peters' response to our report is a classic example of this. Twice now he has publically slammed the report. But he has offered nothing to back up his criticism other than his experience at service stations and a dated OECD report warning of possible labour market problems that have not appeared so far.

If the public want a more rational and level headed discussion on immigration the onus is on us to demand politicians play by this new rule. Insisting that migration debates be accompanied by facts is a great way to start forcing them to do so.