The 2016-2019 parliament saw Australia's worst failure of national opinion polling since the early 1980s, a failure that was not just a combination of normal errors and a reasonably close election. Aggregated polling had the Coalition behind for the entire term, at no stage better than 49% two-party preferred, and yet the Coalition won with 51.53% of the two-party preferred vote.
The view that the polls were in fact right all along but voters changed their minds at the last moment (either on election day, or on whatever day each elector voted) fails every test of evidence that it can be put to. The difference between voting intention for voters voting before election day and on election day is similar to past elections, and if anything slightly stronger for the Coalition. There was no evidence in polling of change in voting intention through the final weeks, as would have been expected as voters who had already voted reported back their behaviour if the polls were at all times accurately capturing the intentions of the person being polled. Also if those who had already voted had shifted towards the Coalition as they made their final decisions while those who had yet to vote were yet to do so, there would have been polling gaps of several points between those who had already voted and those yet to do so; this was not the case in the released evidence either.