Parallel (or mixed) systems use both Proportional Representation (PR) lists and 'winner-take-all' districts. However, unlike MMP systems (see Single Transferable Vote), the PR lists do not compensate for any disproportionality within the majoritarian districts.
Parallel systems are currently used in twenty countries, and are a feature of electoral system design in the 1990s - perhaps because, on the face of it, they appear to combine the benefits of PR lists with single-member district representation. The Cameroon, Croatia, Guatemala, Guinea, Japan, South Korea, Niger, Russia, the Seychelles, and Somalia use First Past the Post (FPTP) single-member districts alongside a List PR component, while Albania, Armenia, Azerbaijan, Georgia, and Lithuania use the Two-Round System for the single-member district component of their system. Andorra uses the Block Vote to elect half its MPs, while Tunisia and Senegal use the Party Block to elect a number of their deputies. Taiwan is unusual in using SNTV, a Semi-PR system, alongside a PR system component.
The balance between the number of proportional seats and the number of plurality-majority seats varies greatly. Only in Andorra and Russia is there a 50/50 split. At one extreme, eighty-eight percent of Tunisia's parliamentarians are elected by the Party Block, with only nineteen members coming from PR lists. At the opposite end, 113 of Somalia's seats are proportionally elected, and only ten are based on FPTP districts. However, in most cases the balance is much closer. For example, Japan elects sixty percent of MPs from single-member districts, with the rest coming from PR lists.
See case studies on Japan - Electoral Reform, Russia - An Evolving Parallel System and Ecuador: The Search for Democratic Governance.
