Parties, Candidates and Citizens On-Line - Åbo Akademi

Appendix A: detailed description of the QCA technique
In practice, the QCA analysis starts with a construction of a so-called ‘truth table’ in which the
theoretically possible combinations of the values of dichotomous independent variables are depicted along
with the empirical outcomes on a dichotomous dependent variable found in the case material (see Ragin
1989: 90). The truth table contains information about the settings in which the dependent variable occurs
or does not occur. In describing these settings, two logical separators are used; Boolean addition and
multiplication. Addition stands for a logical or and multiplication stands for a logical and. Also, the absence
of an independent variable is indicated in lower-case letters, and the presence is indicated in upper-case
letters. Together the settings form a Booelan expression as follows:
F = 1 when Abc+aBc+abC+ABc+AbC+aBC+ABC
This expression is called a ‘primitive’ or unreduced Boolean expression. The expression shows all
combinations of variables in which the dependent variable occurs. The Boolean technique then proceeds
through combining expressions which only differ in one causal condition but produce the same outcome
and reducing them into simpler expressions. For instance, Abc and ABc only differ in the B term but
produce the same outcome, thus B is considered redundant for the outcome on the dependent variable,
and the expression is reduced to Ac. This is repeated for all possible pairings until no further reductions
are possible. In the hypothetical scenario this would result in six reduced expressions: Abc+ABc=Ac;
Abc+AbC=Ab; aBc+ABc=Bc; abC+AbC=bC; ABc+ABC=AB and AbC+ABC=AC. Thereafter, the
process is repeated with the reduced expressions in order to find even simpler expressions. This would
result in two further reductions; Ac+AC=A and Ab+AB=A. Thus, in this hypothetical scenario,
Condition A seems to be sufficient for the occurrence of the dependent variable.
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