Arts & Culture
Proportional Representation and Party System Fragmentation
Quick fact
Countries using proportional representation (PR) tend to have more parties than those using winner-take-all systems; a low electoral threshold can help small parties win seats in parliament.
Why this is interesting
Why do some countries have just two major political parties, while others have dozens? The answer lies in how votes are counted.
Read the full explanation
Understanding Proportional Representation and Party System Fragmentation
Imagine a pie representing all the votes cast. In a majoritarian system, the pie is cut into one big slice for the winner and nothing for the rest. In proportional representation, the pie is cut into many slices proportional to each party's share of the vote. Because PR doesn't force voters to choose only between two main contenders, smaller parties have a real chance to win seats. This encourages more parties to form and voters to support them, leading to a more fragmented party system with more parties represented in the legislature.
A deeper explanation
The mechanism behind this is the electoral threshold and the proportionality of vote-to-seat conversion. In PR, seats are distributed across multiple members per district, so the share of votes a party gets translates directly into a share of seats (assuming no high threshold). This reduces the 'wasted vote' phenomenon that forces voters to abandon small parties. As a result, political entrepreneurs can start new parties that represent niche interests, and voters are more willing to vote sincerely for them. Over time, the party system fragments into more numerous, smaller parties. The effective number of parties index captures this fragmentation. However, if the electoral threshold is high (e.g., 5%), fragmentation decreases because very small parties cannot pass the threshold. Thus, the degree of fragmentation is not just a function of PR but of the specific electoral rules within the PR system.