The Northland by-election did not sharply change national public opinion in the following month, according to the average of the four opinion polls taken in April.
Apart from New Zealand First, the changes in National's, Labour's and Greens' average support were within a range that is not unusual month-to-month.
The four April polls show that while National resoundingly lost the Northland by-election, it did not lose ground in the nation. In the four polls taken up to early March it averaged 47.5 percent. In the four latest polls it averaged 47.2 percent, within a whisker of its 47.0 percent election score in 2014.
The latest four polls were almost all before John Key's ponytail escapades became public. Some unpublished polling in the immediate aftermath of that episode records a sharply less favourable personal rating but whether that is a blip or will last will have to wait a month or two.
Labour plunged in Northland. Its nationwide average fell - but only by 1.4 percentage points, from 31.1 percent up to early March to 29.7 percent and there is some indication in individual poll readings that it may have troughed. It was still above its dismal 25.1 percent 2014 election result.
The Greens' movement was negligible, up from 11.2 percent to 11.5 percent. Its 2014 election score was 10.7 percent.
New Zealand First did get a lift from the by-election win but not (at least not yet) a big bounce, despite Winston Peters' higher profile and higher preferred prime minister ratings.
Up to early March the party was averaging 5.8 percent. After the by-election it averaged 7.3 percent - up by the amount Labour (which told its supporters to vote for Peters) was down. That is still below its 2014 election score of 8.7 percent.
National's lead over the combined Labour-and-Greens score also held firm - 6.0 percent compared with 5.2 percent before the by-election. But that is only about half its 2014 election lead. If anything, the trajectory is down.
Explainer: The Poll of Polls is an arithmetical average of the four most recent major polls since the election from among: TV1 Colmar Brunton, TV3 Reid Research, Fairfax Media-Ipsos, NZ Herald DigiPoll, Roy Morgan New Zealand and UMR Research, which is not published. The four polls in the most recent average were, in order of interviewing, TV1, DigiPoll, Morgan and UMR. The first point on the charts is the actual election result and the polls averaged in the next three points straddled the election. The first point for which all polls were taken after the election is in mid-November.