Additional-member system
The additional-member system (AMS) is a two-vote seat-linkage-based mixed electoral system used for elections to the Scottish Parliament in the United Kingdom, although not for Westminster elections, in which most representatives are elected in single-member districts (SMDs), and a fixed number of other "additional members" are elected from a closed list to make the seat distribution in the chamber more proportional to the votes cast for party lists. It is a form of mixed-member proportional representation and is distinct from using parallel voting for the list seats (also known as the supplementary-member system) in that the "additional member" seats are awarded to parties taking into account seats won in SMDs (referred to as compensation or top-up) – these are ignored under parallel voting, which is a non-compensatory method.