All democratic voting systems create incentives and disincentives which affect the behaviour of political parties and election candidates. It is well-established that different types of voting system can affect the nature of democratic representation and the composition of government. For example, countries which use a voting system based on proportional representation are more likely to have smaller parties represented in their legislatures, to have a multi-party governments, and to have representation from a variety of social groups. On the other hand, smaller parties find it more difficult to win seats under a simple plurality voting system, there tend to be single-party majority governments elected under that system, and the make-up of the legislature tends to be less diverse than in proportional systems.

However it is not only the type of voting system that is important. Variations within types of voting systems can also affect parties' chances of winning seats, and can affect the extent to which members of various social groups are present in the legislature. For example

• What criteria do parties have to meet to be eligible to contest an election? Do these criteria allow new parties to be formed and to compete with established parties on an equal footing?
• Is there a formal or effective threshold or share of the vote which parties have to cross to win seats? Is that threshold set at a reasonable level? Is it applied on a local, state, regional or national basis?
• Do voters elect representatives directly or indirectly through voting for parties? Are seats won or allocated to parties on a local, state, regional or national basis?
• What methods and criteria are used to decide electoral district boundaries? Are they more favourable to some parties than to others?

The choices of the type and details of the voting system used to elect a legislature can thus raise significant integrity issues. But it must always be remembered that there is no perfect voting system. Although it is important that a democratic voting system should be fair, equal and transparent, those goals can be achieved in different ways. It is a matter for each country to judge which voting system will best achieve them in the context of its own history, culture and traditions.

Integrity issues are also raised concerning the process by which decisions are made about changing from one type of voting system to another. For example:

• who should decide that a change is to take place?
• who should design an alternative system?
• how should the final decision be made?
• what opportunities should the public and political parties have to influence the design of a new voting system and the decision-making process?

In 1993 New Zealand changed its voting system for parliamentary elections from the First-Past-the-Post system (FPP) to a system of proportional representation based on the German model, known as 'Mixed Member Proportional' (MMP)⁴¹⁶. This paper outlines the way that change took place. It is not intended that New Zealand's process and experience should be taken as the model which other countries should follow. Rather the New Zealand experience is presented as a case study of why one country decided to change its voting system and the process by which the decision was made.

Why did New Zealand one of the world's oldest democracies make such a major change in its constitutional arrangements, from its well-established single-member plurality voting system to the MMP system of proportional representation?

Three sets of circumstances help explain that change:

1. Election results

2. Royal Commission on the Electoral System

3. The political context

The 1992 referendum [a non-binding national referendum on electoral preferences]

The 1993 referendum

The transition to MMP, 1993-1996 and the The two MMP elections

Effects of MMP

Lessons from the change to MMP

Conclusions