In the STV system, voters rank candidates in order of preference. Votes are then transferred to candidates based on these preferences until a candidate reaches the required quota of votes to be elected.

The STV system allows voters to rank candidates in order of preference, which gives them more choice and ensures that their vote is not wasted if their first-choice candidate is not elected.

The STV system is a complex voting system that can be difficult for voters to understand. This can lead to confusion and errors when casting votes.

The STV system is used in Ireland, Australia, and New Zealand.

The AV system is a preferential voting system in which voters rank candidates in order of preference. If no candidate receives a majority of first-preference votes, the candidate with the fewest votes is eliminated and their votes are transferred to the remaining candidates based on voters' second preferences.

The AV system allows voters to rank candidates in order of preference, which gives them more choice and ensures that their vote is not wasted if their first-choice candidate is not elected.

The AV system can lead to long and drawn-out elections, as it may take several rounds of counting to determine the winner. It can also result in the election of minority governments, as the winning candidate may not have a majority of the votes. Additionally, the AV system is more expensive to administer than other voting systems.

The AV system is used in Australia, New Zealand, and the United Kingdom.

The PR system is a voting system in which seats in a legislature are allocated to parties based on the proportion of votes they receive. This ensures that all parties have a voice in the legislature, regardless of their size.

The PR system ensures that all parties have a voice in the legislature, prevents the election of candidates with a small majority, and encourages cooperation between political parties.

The PR system can lead to weak and unstable governments, make it difficult for voters to hold politicians accountable, and is complex and difficult to understand.

The PR system is used in Germany, Sweden, Norway, and many other countries around the world.

The MMP system is a voting system that combines elements of the FPTP and PR systems. In an MMP system, voters cast two votes: one for a local candidate in their constituency and one for a party list. Seats in the legislature are then allocated based on the proportion of votes received by each party, with some seats reserved for local candidates.

The MMP system combines the benefits of the FPTP and PR systems, ensuring that all parties have a voice in the legislature and preventing the election of candidates with a small majority.

The MMP system can be complex and difficult to understand, can lead to weak and unstable governments, and can make it difficult for voters to hold politicians accountable.

The MMP system is used in New Zealand.