The Overhang on NZ polling

The Overhang has a long and useful article about polling in NZ. Their summary is:

• Opinion polling in New Zealand elections has historically been reliable and in the absence of other information can be trusted as a guide to voters’ behaviour.
• Rather than emphasising any single poll, it is better to: look at them in aggregate and think in terms of probability.
• Relative to each other, certain polling firms do persistently overrate or underrate some parties in a statistically significant way (house effects). 
• Polls can change, sometimes rapidly, even this close to an election.

They do their normal house effects calculation:

And the consensus trend: