Proportionality

How population growth affects the number of electorate seats

Since 1965 when the number of South Island general electorates was fixed at 25 (and now, under MMP, at 16), the number of North Island general electorates has increased after every five yearly census (and the number of Māori electorates increased with the introduction of MMP and after the 1996 and 2001 censuses).

This is due to the disproportionately faster population growth of the North Island compared to that of the South Island. The table below shows this increase under both the previous First Past the Post voting system and MMP.

Assuming this trend continues there will come a point in time when the number of list seats will be too small to continue to be compensatory and thus may not guarantee proportionality.

• When might proportionality be affected?

  In 2000 the Department of Statistics provided a table projecting the total number of electorates to the year 2051. Using projections for population growth over 50 years, the maximum number of electorates was estimated to reach 77 for both general and Māori electorates (and the number of list seats would reduce to 43).

  A formula used to estimate when the number of list seats will no longer be sufficient to ensure proportionality is when the ratio of the proportion of a party’s electorate seats to the proportion of party votes exceeds the ratio of the total seats in Parliament to the total number of electorate seats. On this basis, proportionality will probably not be affected by a 77/43 mix of electorate and list seats.

  Note: The Department of Statistics table was provided to the 2001 select committee review of MMP.

   

• How the number of electorates is determined in New Zealand

  Sections 35 and 36 of the Electoral Act 1993 require the division of New Zealand into general seats between the North Island and the South Island. Section 45 of the Act provides for the Māori seats to be determined in a similar way. This division takes place after each census.

  The Representation Commission is the body responsible for this division. The following steps must be taken:

  • The South Island is to have 16 general electorates;
  • The South Island general electoral population is divided by 16 to give the South Island quota (the general electoral population for each electorate);
  • The North Island general electoral population and the Māori electoral population is then divided by the South Island quota to give the number of North Island general and Māori electorates (a figure of .5 or above is rounded up);
  • The North Island general electoral population is divided by the number of North Island electorates to give the North Island quota;
  • The Māori electoral districts must each contain an equal number of members of the Māori electoral population;
  • No general electorate is to be partly in both the North and South Islands;
  • Electoral boundaries are drawn taking into account the existing boundaries and communities of interest, facilities of communication, topographical features and any projected variation in the electoral population of those districts (and, alternatively for Māori electorates, tribal affiliations).

  The table below shows how this worked in practice after the 2006 census.

  Steps	Electoral population	Number of electorates
  South Island general electoral population (SI-GEP)	920,999
  Divide the SI-GEP by 16	57,562	16 (determined by law)
  North Island general electoral population (NI-GEP)	2,690,437
  Divide NI-GEP by 57,562	46.739	47 (rounded up)
  Māori electoral population (M-EP)	417,081
  Divide M-EP by 57,562	7.245	7 (rounded down)
  Total electorates In a 120 seat Parliament, 50 list seats are required (list seats equals 120-70=50)		70