Fuzzy-Set Analysis

Claudius Wagemann

Fuzzy-set analysis (FSA) is one branch of qualitative comparative analysis (QCA). The idea of fuzzy sets goes back to earlier insights from computer science and formal logic, which had led to the development of a fuzzy-set approach already in the 1960s. As George Klir, Ute St. Clair, and Bo Yuan (1997) have shown, the difference between fuzzy sets and conventional (“crisp”) sets is that set memberships are unequivocal in crisp sets. For example, the element “Sunday” is a member in the set of all days of the week (membership value of 1); whereas the element “January” is not a member of that same set (membership value of 0). By contrast, fuzzy sets have the characteristic that nonperfect set membership can exist. This is especially relevant considering that social science concepts very often have fuzzy boundaries. Democracies are usually not perfect democracies but just democracies to a certain degree. Following this ...

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