Proportionality for Solid Coalitions facts for kids

Proportionality for Solid Coalitions (PSC) is an important idea for voting systems. It helps make sure that different groups of voters get a fair share of elected representatives. This is especially true in elections where many winners are chosen, like for a city council or a parliament. It's all about making sure everyone's vote counts in a balanced way.

What Are Solid Coalitions?

Imagine a group of voters who all agree on certain candidates. This group is called a solid coalition. For example, if a group of friends all want the same three people to win an election, and they rank those three people higher than anyone else, they form a solid coalition.

This idea helps us understand how different groups of voters can work together to get their preferred candidates elected.

Understanding Proportionality in Elections

In elections, "proportionality" means that if a certain percentage of people vote for a group of candidates, then roughly that same percentage of seats should go to those candidates. For example, if 30% of voters support a certain political party, that party should ideally get about 30% of the seats.

PSC helps make sure this happens, especially for groups of voters who strongly support a specific set of candidates.

How PSC Works with Quotas

To figure out if an election is proportional, we often use something called a "quota." A quota is a number of votes needed to win a seat.

One common quota is the Hare quota. You get it by dividing the total number of voters by the number of seats available.

• If a solid coalition has enough voters to meet a certain number of Hare quotas, then they should win at least that many seats.
• For example, if a group of voters is large enough to meet two Hare quotas, they should get at least two of their preferred candidates elected.
• This idea was first suggested by Michael Dummett.

The Droop Proportionality Criterion

Another way to measure proportionality uses the Hagenbach-Bischoff quota, which is also known as the Droop quota. This quota is a little smaller than the Hare quota. You get it by dividing the total number of voters by the number of seats plus one.

• Using the Droop quota, if a solid coalition has enough voters to meet a certain number of Droop quotas, they should also win at least that many seats.
• This method is often called the Droop proportionality criterion.
• It's a more general way to ensure that large groups of voters get a fair number of seats. For instance, a group of voters that makes up a majority (more than half) of all voters should always be able to elect at least half of the available seats.

See also

In Spanish: Proporcionalidad por Coaliciones Sólidas para niños