Western Europe
Electoral Systems

Plurality Systems

US, UK, France (with the two ballot twist)

Single Member Districts

i.e., geographical representation
“first past the post”

winner take all system

the most votes wins

Pros of Plurality System:
Allows for geographical interests to be represented

Good for countries with a lot of geographical diversity, regional sub-cultures

Tends to produce majority Governments, i.e., in parliamentary systems, the winning party can usually form a Government on its own, without forming coalitions with other parties

Creates very centrist parties, as in the US, especially (some would see this as a virture, others a vice, see below)

Cons of Plurality System:
Creates very centrist (rather than programmatic) parties!

Disadvantages “third parties” as well as more ideologically extreme parties (again, this can also be deemed as an advantage as it keeps the “nut cases” out of parliament)

Can create rather large discrepancies between percent of vote obtained by each party nationally (i.e., aggregated at the national level) and the proportion of seats that party wins in parliament (e.g. can win 49% of the vote in every race and get NO seats)

Proportional Representation:

Most continental parliaments are elected this way, including Germany’s and Italy’s, where some of the seats are elected geographically by plurality, and some are elected proportionally from party lists)

The idea is that the number of seats won by each party more closely mirrors the popular vote

This is often accomplished via
Multi-Member Districts

each constituency elects several representatives, allowing the block of votes to be distributed . This is more precisely done, the more seats there are to distribute. 

The Netherlands is the purest example of this as it votes as one large national constituency

In most countries, thresholds are used to prevent over splintering of the parliament

In other words, you must get some minimum percent of the national vote in order to qualify for a party list seat

Typically thresholds are between 3 and 5%

Cons of PR systems:
In highly proportionally systems, it can lead to a lot of “coalition governments,” i.e., the situation where the largest vote getting party doesn’t have a majority and must form coalitions with other parties.

In some cases “minority governments” are possible, when a party that got less votes than the winning party but still can form a government either because other parties team up against the winning party or because the winning party itself cannot put together a governing coalition.

This, BTW, is how Hitler and the Nazis gained power in Germany in 1933; The Communists wouldn’t cooperate with the more mainstream parties so Hitler and the National Socialists were able to form a government alone

In general, PR systems are more instable IF there is a strong history of partisanship, regionalism, discrete geographic interests, a high degree ideological polarlization, etc. (e.g. Italy from WWII til the 2008: it has had a total of 65 governments!)

PR can reify ideological differences, partisanship in the absence of traditions of moderation or elite compromise

Pro or Con Depending on the Party:

Allows for minor parties to become members of coalition governments _ giving them, perhaps, more voice than their percentage of the vote entitles them (e.g. the Greens in Germany’s 1997-2005 governments)

Pros of PR systems:
Closer correspondence between national vote and distribution of seats
Allows from more programmatic or ideologically different parties (i.e. _third parties_ are not punished; rather rewarded)

Variations on a Theme
The French two ballot system
First round is vote among candidates from all parties _ perhaps a dozen
If someone wins a majority, the game is over
If no one wins a majority _ there is a run-off
In parliamentary races, anyone with more than 12.5% goes on to second round.  In presidential races, only top two (guaranteeing the winner a majority)

In plurality systems: single transferable votes
Also called “alternative” or “preference voting”
Voters rank-order their choices so that it’s more likely for everyone’s second choice to emerge as the winner