The Donald Trump presidency polls couldn't predict

US President-elect Donald Trump (Reuters)
US President-elect Donald Trump (Reuters)

So Donald Trump is the new US President - who could have predicted that? Definitely not the polls.

If the countless polls were to be believed, it would be Hillary Clinton walking into the White House, so how did the pollsters get it so wrong?

There are a number of theories being bandied about as to how election day results were at odds with the perceived mood of the country in the lead up to voting day.

National Party pollster, Curia Market Research principal and blogger David Farrar says the reason polls were so out will be the focus of a serious debrief by polling companies - "everyone wants to know that".

But there were generally two reasons why polls are wrong - the first is people don't vote for who they say they will.

"I think that may be part of it, but I'm a bit sceptical that's a major part because in some states it was quite accurate, other states it wasn't and with online polls or robo-polls where it is voice-activated, while they're not as accurate in some regards its thought people are more likely to tell the truth if it's not a human being they have to admit voting Trump to."

The bigger problem is if companies have their sampling groups wrong.

But Mr Farrar believes the mistakes in the polling were part of an election which was full of unpredictability.

"It's not just a polling error, everything in the model didn't work. The democrats had the most sophisticated ground game ... Trump spent more on hats than polling, he basically made a series of speeches around the country and tweeted a lot and won."

He says in more conventional elections, polling is generally more precise.

"This is just the most freakish election you'll ever see."

The Trump result wasn't the only major world event the polls got wrong this year. They also failed to predict the outcome of Brexit, where voters chose to leave the European Union.

"[That] was closer, they had an average for 2 percent [majority] for remain and it was 2 percent [majority] to leave, but was within the margin of error," Mr Farrar says.

"The more conventional elections where it's not so much a life or death decision tends to be more accurate, but when it's a more fundamental 'do we stay in the EU?', 'do we elect Donald Trump?', the model gets more broken."

Reid Research managing director Ngaire Reid believes it could be a result of what's plaguing the polling industry - getting in contact with people.

There was one poll which had Mr Trump in the lead consistently for the final months of the campaign - a result called an "outlier" by other media at the time.

The 'Daybreak Poll', done by the University of Southern California (USC) and the Los Angeles Times, turned out to be one of the very few which turned out to be right and that's because of the "unconventional" method.

"It has been an unusual election year, with unconventional candidates and campaigns - and our unusual poll," USC Centre for Economic and Social Research director Arie Kapteyn and survey director Jill Darling said.

The poll sought to measure participants' level of certainty in their plan to vote for candidates on a scale of 0 to 100 and how committed they were to a candidate. That's different to more traditional polls which ask for a candidate preference or who they'd vote for.

Documentary filmmaker Michael Moore was also one of the few who called the race for Trump - he made the prediction in July.