In 1999 the Labour Government won 39% of the vote. The next poll had them at 50%. So they got an 11% bump from winning.
It lasted a year. By October 2000 they were back to 40%.
In 2008 National won 45% of the vote. The next poll had them at 56%. SO also an 11% bump from winning.
So both recent changes of Government has seen an 11% bump for the winning party. This is because people like to give a new Government a fair go.
If this Government follows form, then the next public polls should show Labour at 48%. What will be interesting is where any increase comes from.
The other thing that will be interesting is how long the bump lasts for. In 2000 it lasted a year. But National’s bump lasted their entire first term – they never dropped below 49% in the One News Colmar Brunton poll. Will Labour’s bump last for a year, less than a year, or more than a year?