The Schulze Method – Agora 101

By | September 24, 2017 at 9:00 am | Agora, European Events | Tags: , , ,

During Agora, there can be many scary words going around if you’re there for the first time – especially if you’re a delegate. Don’t worry, the Chair Team is here for the rescue! In this article, the Schulze method (ranked voting) will be explained, so you can come a bit more prepared.

 

What is ranked voting?

Ranked voting is a type of online voting where instead of simply casting votes, delegates are asked to rank their preferences. It is currently used for the EPM topic selection, and was used for selecting the Focus Areas for Strategic Plan 2017-2020 (in combination with voting on the number of focus areas). Ranked voting was introduced to the CIA by a proposal in Agora Bergamo, and has been used in practice since Agora Chisinau.

 

What is the Schulze method?

The Schulze method is a specific way of ranked voting which is in the CIA used for ranked voting (by the same proposal in Agora Bergamo). It was developed in 1997 by Markus Schulze as an electoral system for selecting a single winner by using votes that express preferences. Without getting into too many details, the method works with the following system: voters make an ordered preference list (aka ranking the options) where ties and/or leaving out options are allowed. Then for every two options, they are compared (ignoring the other options), checking which option is more preferred by the voters. After the options are compared, the system calculates the strongest paths (aka which option is the most preferred overall by all voters) and the final results are made.

 

Looks confusing? Here is an example supported by Wikipedia:

 

Let’s assume that there have been 5 topics submitted for EPM, named A, B, C, D and E. There have been 45 votes cast in the following order:

Number of voters           Order of preference

5                                       ACBED

5                                       ADECB

8                                      BEDAC

3                                      CABED

7                                      CAEBD

2                                      CBADE

7                                      DCEBA

8                                      EBADC

 

First, the pairwise preferences are calculated which will look like this:

schulze1
Green means that the voters preferred the option in the column, red means that the voters preferred the option in the row (for example, 20 voters preferred topic A over B, and 25 who preferred topic B over A).

For the next step, the strongest paths are calculated (how it is exactly done is visualised with direct graphs in the Wikipedia article), which will look like this:

schulze2

Green means that the voters preferred the option in the column, red means that the voters preferred the option in the row (for example, 28 voters preferred topic A over B, and 25 who preferred topic B over A, so with the Schulze method topic A is better than topic B).

Based on the Schulze method, the ranking is E>A>C>B>D, therefore topic E is selected for the topic of the EPM.

How the method is visualised in the AEGEE voting system you can see it in the following pictures:

schulze3

schulze4

schulze5

schulze6

The Schulze method has been selected for voting for the following reasons:

  • It allows the delegates to make ties for the ranking (they can rank one or several options as same importance)
  • It allows the delegates to leave out options (they can leave an option out of the ranking if they feel strongly against it)
  • It reflects on the majority decision (the option which is preferred by most voters in general)

 

We hope that with this article we could give you a bit of help for understanding the Schulze method as ranked voting in AEGEE! In case you have any questions or doubts, don’t hesitate to ask us before Agora at chair@aegee.org, or at the HRC help desk during the Agora!

 

Written by Tekla Hajdu, Chair Team jobshadower


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