Compare and contrast FPTP with AMS and STV

The First Past the Post Electoral system is used in general elections in the UK on a constituency basis in order to elect Members of Parliament. If a party has a majority of the seats in the House of Commons, it has the right to form a government. To win a seat in the FPTP system, one must only have one more vote than the second most popular candidate. It is considered to be a highly majoritarian system, by contrast to AMS and, to an even greater extent, STV. The Additional Member System uses FPTP to elect MPs in constituencies, although these are generally larger than under a purely FPTP system. However, there are more seats in Parliament than there are constituencies; the remaining ones are proportionally filled by members of political parties according to the results of an added part to each ballot, in which voters choose their preferred party. This system, used in elections for the Scottish Parliament, falls somewhere between FPTP and STV in terms of proportionality. The Single Transferable Vote system, works on the basis of multi-member constituencies, which are even larger than AMS constituencies. Voters rank candidates according to their preference of representative. When votes are counted, any candidate with a majority of the vote automatically gains a seat. Any votes past the fiftieth percentile are redistributed according to second preference amongst the remaining candidates. If no candidate achieves a majority, the candidate with the least votes is eliminated and their votes are redistributed, These combined processes are repeated until all the seats in the constituency are filled. This system is used to elect the Northern Ireland Assembly.