Additional Member System
USED IN: Germany, New Zealand, the Scottish Parliament, Welsh Assembly
HOW IT WORKS: Voters have two votes - one for normal constituencies which are elected by First Past the Post. The other is for a List system - parties get extra MPs to top up their group in Parliament until they have the number of seats proportionate to the number of votes they have received.
PROS: Maintains the link between constituencies and MPs, while also being proportional.
CONS: Can give third parties unproportionate influence by giving them the balance of power, and can make it difficult for one party to govern.
(Graph allows for a 50:50 split between the constituency and list systems)