the parliament is elected by a mixture of the first past the post and proportional representation electoral systems, namely, the additional members system. thus the parliament is unlike the westminster parliament, which is elected solely by the first past the post method. the scottish parliament is elected every four years and has 129 members, referred to as members of the scottish parliament (msps). of the 129 msps, 73 are elected to represent first past the post constituencies, whilst the remaining 56 are elected by the additional member system.