Supplementary Member(SM) is a semi proportional electoral system. In this system the majority of parliament is filled with the winners of electorates, the remaining quarter of parliament is then selected from party lists in proportion to each parties share of the vote. a party which gets 40% of the vote but somehow wins no electorates will only get 10% of the seats in parliament(40% of the list seats).
1996
The citizens of Hamilton East decided that the Sm system would be sufficient to hold the large parties to account, only time would tell whether this would be reality.
In the first election under this new system a variety of parties were represented in parliament, however National held almost three quarters of the seats in parliament and were able to enact their policies without consideration of any other party.
1999
In 1999 a few of the smaller parties were eliminated and the Greens arrived in parliament, Labour and their natural allies increased their share of the vote but were unable to defeat National which had a one seat majority and was able to continue governing alone.
2002
the 2002 election saw the Alliance removed from parliament while New Zealand First and United Future entered. Labour managed to gain a majority of parliament and governed alone.
2005
The 2005 elections saw all the minor parties except for New Zealand First and the Greens removed from parliament, National also managed to regain a majority of parliament and was able to govern alone.
2008
After the 2008 election the Greens were the sole surviving minor party, National was able to slightly increase its lead over Labour.
Table of Results
Summary
In this example SM returned a single party government in all the elections, while it does give minor parties representation they were unable to exert any influence on government. In all the elections the two largest parties were over represented while the smaller parties were under represented. Again large swings can be seen, although not as large as under FPP or PV, the 1 point decline in Labour’s vote between 2002 and 2005 results in them losing 19 % of parliament to National
