Appendix B. Overview of QCA
Qualitative comparative analysis (QCA) refers to a range of analytical methods grounded in set theory. One distinguishing characteristics is that QCA is not a statistical method but one that is based on logical relations between sets. As Rihoux and Marx (2013 p. 168) explain: “A set theoretic approach starts from the idea that attributes of cases are best described in set relations and not in terms of variables. Variables aim to capture a dimension of variation across cases and distribute cases on this variation. A set assesses whether, or to what degree, a case is a member of a set and then analyses the intersection between sets.” As an illustration, consider an example with two MC practices (A and B) hypothesized to have an association with MC effectiveness (Y) (Bedford & Sandelin, 2015). Assuming that each MC practice can take only one of two values, either 1 or 0 to indicate high and low use, then there are a total of four possible combinations (i.e. sets) to which a firm can be a member. Using set-theoretic notation, where “~” refers to the logical operator not and “” denotes the logical operator and, the possible sets in this example are AB, A~B, ~AB, and ~A~B (e.g. the second set refers to the combination of A and not B, which corresponds to a high use of practice A and a low use of practice B). Firms in each set may have either the outcome of high MC effectiveness present (Y) or absent (~Y). The analysis proceeds by examining the overlap between firm membership in the sets of MC practices and the outcome. These relations are displayed graphically in Fig. 1. In this example the set of firms that combine a high use of A with a high use of B have the greatest overlap with the set set of firms with high MC effectiveness (Y). This suggests that firms with the combination AB consistently achieve the outcome while firms with other combinations do not.