The Schulze method is a way of voting that is used to fill a single vacant position in an election. It was developed in 1997 by Markus Schulze. It is also known as Schwartz Sequential Dropping (SSD), Cloneproof Schwartz Sequential Dropping (CSSD), Beatpath Method, Beatpath Winner, Path Voting, and Path Winner. It is used by several organizations including Debian, Gentoo, BerryTube, and the KDE team. Wikimedia used to use it before switching to the simpler score voting.
Voters rank the candidates in the order from the one that they most want to win to the one they least want to win. The same preference (how much the voters want the candidate to win or lose) can be given to more than one candidate, and candidates can be given no number (they are interpreted as the worst).
Next, for every pair of two candidates, the two are compared: ignoring all other candidates, which of the two in the pair is preferred by most voters? How many voters agree with the majority decision is noted.
More calculations take place. Given two candidates A and K, A is said to beat K with strength t if t voters prefer A to B, t voters prefer B to C, and so on, and t voters prefer J to K. The winner W is the candidate which beats any other candidate X with strength t, but X does not beat W with strength t.
