Do party preferences change during an Election Year?

Another excellent post by Gavin White at UMR’s SayIt blog.

Gavin’s analysis of both UMR and Colmar Brunton poll results going back to 1993 and 1996, respectively, shows that party preferences do actually change considerably during an Election Year.

“I’ve heard it argued from time to time that party votes don’t tend to shift much in election year, when in actual fact nothing could be further from the truth.  I looked at UMR polls back to 1993, Colmar Brunton polls back to 1996, and other public polls since those dates, where they were available.  I simply compared the first poll of election year with the actual election result, and here’s what I found

– The vote for the incumbent party (i.e. the main party of government at the time) has fallen during election year at 6 of the last 7 elections.  It has fallen by an average of 5%.

– The vote for the party leading the polls at the beginning of election year has fallen by the election for every one of those seven elections.  The average decline is 6%.

– The major beneficiaries of those drops have generally been minor parties (e.g. United Future, NZ First and ACT in 2002, NZ First in 2011).”

In another post, Gavin examines poll results industry-wide to show that, on average, the final mainstream media polls prior to elections have tended to get a result:

  • 2.4% too high for National
  • 0.5% too low for Labour
  • 1.5% too high for Green
  • 1.1% too low for NZ First

That’s an average across all polls, so some will have results in the opposite direction, or more strongly in the same direction, for some parties. Another difference I think it’s good to note is that some polls appear to be more volatile than others, at different times, which can sometimes make it hard to know if support is increasing or decreasing at any given time. There could be a number of reasons for this. I really dislike poll volatility – makes it impossible to detect the signal for the noise.

UPDATE: Corrected some typos.

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