What are the most important differences between a single-member district and proportional representation? What is more democratic? Which is more efficient? Which do you prefer and why?
Systems of single member and proportional representation are very different. Single member representation, as in the United States, works by carving every state in the country into individual districts based upon population density. In the United States, the number of one-half of a million people is the rough number of citizens in each district. As states lose population for any reason, such as a major decline in job opportunities to other states, they lose voting districts. The number of districts and, consequently, the number of elected officials in the House of Representatives (under the U.S. Constitution, each state has two senators) representing each state is determined on the basis of the national census taken every ten years. Populations shifts, therefore, determine which regions gain and which regions lose representation.
Each district in each state has one elected official serving in the U.S. House of Representatives. That elected official only needed to get a plurality (more than any other candidate) of the votes cast in his or her district to win the election. Because of the overwhelming advantage maintained by the two major American parties, the Democrats and the Republicans, candidates from these parties usually win their seats with a majority of the votes cast by their voting-age constituents. It is possible, however, for an elected official to have enjoyed only a plurality of the votes cast when a third party draws votes away from one or both of the two larger parties.
In a system of single member representation, then, every group of citizens has a single elected official representing it in the House of Representatives or similar legislative body. In a system of proportional representation, the total vote across the nation or district in question determines the percentage of elected officials from each party serving in the legislature or parliament. In other words, each individual party's percentage of seats in the legislature is determined by the percentage of votes that party receives the election.
An argument can be made that the proportional representation model is more democratic because it is open to more political parties. In the single member representation model, only the candidate with the most votes, whether that member prevailed with a majority of votes or with a simple plurality, wins a seat. This sometimes results in split elections where the least popular party in a district wins the election (e.g., if two liberal candidates each received 30% of the vote and a conservative candidate wins with only 40% of the vote). In a system of proportional representation, the smallest political parties receive seats in the legislature if the party in question receives enough votes to qualify for seats (using the example above, 30% of the district's seats would be allocated to each liberal party, 40% to the conservative party, etc.). In that sense, it represents the more democratic model, as a far broader spectrum of perspectives or ideologies is present.
There are benefits and drawbacks to each method. While the model of proportional representation allows for a broader array of parties and perspectives, proportional systems work best in districts with a large number of seats or nation-wide elections. On the other hand, the larger parties in the single member system may struggle to deal with ideological diversity. We see this tension in the current Democrat and Republican parties, both of which have been fractured by increasingly vocal elements wishing to shift party platforms in different directions.
A single member district is an electoral district from which only one person gets elected in a given race. All Congressional districts in the United States are single member districts. It is true that two senators are elected from each state, but they do not run in the same race. They are elected in separate races where only one person can win. So, in a single member district, only one person (the one who gets a plurality of the votes) wins the election and gets to hold office.
In proportional representation, each district is represented by more than one person and all the representatives are elected in a single election. For example, a district might have 10 representatives in a legislature. Each party submits a list of 10 names to fill those spots. The people vote for parties, not for individuals. The votes are counted and the parties get representatives based on their proportion of the vote. If Party A gets 40% of the vote and Party B gets 10%, Party A gets 4 of the representatives and Party B gets 1 (with other parties getting the other 5).
Many people would argue that proportional representation (PR) is more democratic. They would say that PR allows more voters to actually have a say in elections. In a single member system, a party that gets 20% of the vote will not have any representation. Its members have essentially not been heard. In a PR system, that 20% is heard and represented.
Many people argue that PR is, however, less efficient. In a system that has single member districts, there are usually only two major parties. This means that one party is very likely to have a majority of the seats in the legislature. This allows that party to enact its policies more easily. In a PR system, parties often do not have majorities and have to form coalition governments with other parties. This can make it harder for any one party to push its agenda through the legislature.
As to preferences, that is a matter of personal choice. What do you think? Is it more important to have a government that can get things done fairly easily or is it more important to give representation to people who support small parties?