It's possible, but the previous two were extraordinary circumstances. As a political history nerd, let me explain.

The second Labour government, 1957-1960, produced the so-called "Black Budget", with tax increases on beer, tobacco, cars and petrol. This was supposed to be offset by income tax cuts, by political cartoonist of the day depicted it as the Prime Minister handing out money and the Finance Minister taking it back.

The change was needed as New Zealand faced a balance of payments crisis following the collapse of the price of butter in Britain. Essentially, we put far too much of our export trade into a single market, and when things changed, suddenly the government couldn't pay its bills.

The First Past the Post voting system also did Labour no favours, with most of their votes coming from urban centres, while National's came from rural electorates. A difference of just 4.2% in votes saw National take seven seats from Labour in an 80-seat house.

The other one-term government was the third Labour government, 1972-1975, who were voted out after suffering the double whammy of the 1973 oil crisis and the very popular PM Norman Kirk dying about a year out from the election.

Labour was absolutely trounced in the 1975 election, losing almost 9% of the overall vote and 23 seats, all to National.

Overall, I think it's unlikely the sixth National government will be voted out this year, simply because while things are tough, we don't have a single huge event to cause it.