Under a mixed electoral system, different formulas are used simultaneously to allocate seats from a single election. One feature all mixed electoral systems have in common is that an elector casts two votes, one for a candidate to serve as an electoral district representative and one for a party list of candidates. Among countries with mixed electoral systems, there are variations in the proportion of seats elected by district and the proportion elected by party list. There are also variations in the voting scheme--majority or plurality--adopted for district elections. And most importantly, there are variations in the relationship between district seats and party list seats.
In some countries, the total allocation of seats is based on the number of party list seats minus the number of district seats. In other countries, the allocation of seats is based on the number of party list seats plus the number of district seats. This distinction is crucial for the proportionality of seats to votes.
Mixed Member Proportional Systems
In countries such as Germany and New Zealand, the final seat tally for each party is calculated by subtracting the number of district seats that each party wins from the total number of party list seats to which it is entitled. The party list seats, therefore, are used to correct any unfairness in the single-member plurality or majority seats. This is sometimes called the 'mixed member proportional' system because the results are proportional, provided that a party exceeds any threshold vote percentage that may have been established. For more information on mixed member proportional systems, see Mixed Member Proportional.
Parallel Systems
Countries such as Russia do not subtract district seats from party list seats, but rather add the two sets of seats together. Because the district seats and party list seats are independent of the one another, the party list seats do not correct for any seats due to votes distortions created by the single-member district seats. The results in these mixed systems, sometimes referred to as 'parallel' electoral systems, have tended to be disproportional. For more information about parallel electoral systems, see Parallel.
Conclusion
One advantage of a mixed electoral system is that it uses single-member districts and, therefore, retains a strong link between representatives and their constituencies. At the same time, however, a high level of proportionality may be achieved, although the degree of proportionality is dependent on whether or not party list seats are used to correct for distortions produced by the electoral district seats.
The significance attached to the delimitation of electoral districts in a mixed system depends on whether or not party seats are used to rectify any distortions in the seats-to-votes ratio. If party seats are used to correct imbalances, then the process of delimiting districts is not much of an issue. If, however, party seats are not used as a corrective measure and disproportionate results are possible, the delimitation process becomes more important. In fact, the delimitation process may be as important as in a plurality or majority electoral system.
