qualitative comparative analysis (QCA)
The name given by Charles Ragin (The Comparative Method
, 1987) to his proposed technique for solving the problems that are caused for comparative macrosociologists by the fact that they must often make causal inferences on the basis of only a small number of cases. The technique is based on the binary logic of Boolean algebra
, and attempts to maximize the number of comparisons that can be made across the cases under investigation, in terms of the presence or absence of characteristics (variables) of analytical interest. Thus, for example, 18 cases (say, nation-states) involving 7 independent variables (presence or absence of economic recession, of an external threat to state security, and so on) might be examined in order to identify the causal factors involved in the emergence of revolutions, in this example yielding no fewer than 128 (27
) different combinations of causal conditions. Ragin claims that the technique combines the strengths of case-oriented (qualitative) and variable-oriented (quantitative) approaches to comparative sociology
. Critics argue that it allows only for logical rather than statistical representativeness; makes no allowance for missing variables or error in the data; that not all variables of interest have only two values; and that the method is therefore highly sensitive to the way in which each case must be coded in a binary fashion. For example, the choice between ‘presence of economic recession versus absence of economic recession’ makes no allowance for intermediate conditions, or for the length and severity of recession itself. These coding
problems are heightened where (as is often the case) the researcher is dealing with continuous variables—such as income and the degree of inequality in its distribution—which can obviously be collapsed in different ways.