Comparative Politics/Proportional Representation, Single-Member Plurality, and Mixed Representation
In a proportional representation system, parties are allotted seats in the legislature based on the percentage of the votes that they receive in the polls. Each voter will select a party instead of an individual candidate, after which parties will be assigned seats according to percentages. In many countries there is a threshold that a party needs to pass before getting a seat (generally between 2 - 5 percent). The seats that would have gone to parties receiving under this threshold are divided up by the parties that passed the threshold. Some countries using proportional representation include Israel, Italy, and Iraq.
In a single-member plurality system, members are elected to the legislature from electoral districts. Only one member can be elected from each district. The member who is elected is the person who receives the most votes in that district, even if he does not receive a majority of the vote. Some countries that use this system are the United States and Britain.
In a mixed representation system, some members are elected from electoral districts after receiving a plurality of the vote, while the rest of the seats in the legislature are assigned according to proportional representation. Voters in these countries generally vote for a candidate and a party. Countries employing mixed systems include Russia and Mexico.
A single-member system favors major parties, and will generally allows for only two or three healthy major parties. In the US, for example, only Democrats or Republicans typically win seats; in Great Britain, only the Labour, Conservative, and Liberal parties win seats. This forces the parties to moderate to gain votes and may make compromise in government easier.
A proportional system allows smaller parties to gain seats. This will result in many views represented in the legislature but may make the government less stable. In addition, it may be difficult to employ in a big country because the votes of the entire nation need to be pooled and then divided. A recount in a close election would therefore be impractical.