New Zealand may never have a better chance of drawing top talent away from America. This week's changes to skilled migrant requirements will help but not as much as they should.

The United States has long been a strong draw for the world's top talent, through the combination of an excellent university system and the world's largest economy.

America's immigration system has never been particularly friendly. But, since Trump's election, it has taken a substantial turn for the worse.

Even Silicon Valley tech firms have not been immune. The kinds of immigration raids on factories lampooned in Cheech and Chong's classic Born in East L.A. now happen at tech companies.

Living in America on a skilled migrant visa, their H-1B, would be nerve-wracking. And so New Zealand has a fantastic opportunity to attract skilled workers.

New Zealand's skilled migrant system has been successful. The OECD reports that New Zealand's immigrants are among the most highly skilled in the world. But there are still substantial problems.

Somebody in a ministry has to guess which occupations are sufficiently skilled and in sufficient shortage in New Zealand to be listed in the skills shortage list. Market wages can often give a better indication of shortages than can some bureaucrat's list.

And so the Government's decision to shift from relying heavily on these kinds of lists and to look instead at offered salaries makes a lot of sense.

If someone has been offered a six-figure salary to take a position in New Zealand, that person brings important skills to the country regardless of whether those skills meet ministry box-ticking.

The New Zealand Initiative recommended this kind of change earlier this year in its report, The New New Zealanders.

But there remains another problem.

There are no practical routes allowing a skilled migrant to move to New Zealand without a job offer in hand. Counting the salary that comes with a job offer means the system will better recognise skills, but still requires that the migrant have a job offer before getting here.

And that can be difficult.

Put yourself in the position of an employer considering an applicant based abroad. You need to hire soon.

A candidate who was born in India but who has lived and worked in America on an H-1B visa for a decade has applied.

The candidate beats anybody available domestically, and will have enough points to be granted the visa on being given the job offer.

But the candidate will not be eligible to work until the visa comes through. And getting the visa requires getting a police background check from the candidate's country of citizenship, even if the applicant has not lived there in decades.

When I emigrated to New Zealand, the Canadian Government took so long to process my police background check that my medical certificate expired while I was waiting.

I was lucky enough to be heading to the University of Canterbury, which was not too worried about my start date.

But for other employers, having to hold a position open for months while waiting on a foreign country's police checks can be a deal-killer. The offer is never made.

Immigration Minister Michael Woodhouse is already making changes to make the system work better for skilled migrants. And the opportunity to attract skilled workers currently living in America will not last forever.

New Zealand could do well by easing police background check requirements for those who have already made it through America's immigration system.