Combining QCA and Process Tracing in Set-Theoretic Multi-Method Research

Abstract

Set-theoretic methods and Qualitative Comparative Analysis (QCA) in particular are case-based methods. There are, however, only few guidelines on how to combine them with qualitative case studies. Contributing to the literature on multi-method research (MMR), we offer the first comprehensive elaboration of principles for the integration of QCA and case studies with a special focus on case selection. We show that QCA's reliance on setrelational causation in terms of necessity and sufficiency has important consequences for the choice of cases. Using real world data for both crispset and fuzzy-set QCA, we show what typical and deviant cases are in QCAbased MMR. In addition, we demonstrate how to select cases for comparative case studies aiming to discern causal mechanisms and address the puzzles behind deviant cases. Finally, we detail the implications of modifying the set-theoretic cross-case model in the light of case-study evidence. Following the principles developed in this article should increase the inferential leverage of set-theoretic MMR.

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“…-- Figure 3 about here --We now discuss deviant cases for coverage as part of the explorative logic of QCA, which aims at going beyond a mere testing of theories to improve and refine the concepts and frameworks applied (Rihoux and Ragin, 2008;Schneider and Rohlfing, 2013). Nidwald is the "most deviant case coverage" for enabling integration.…”

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“…Finally, we enhanced the theoretical interpretation of our solutions by adopting a recently developed approach of identifying most-typical cases associated with each solution (Schneider & Rohlfing, 2013). To do this, we relied on graphical representations of case membership of the overall solution and of the outcome, and also identified and analyzed cases not covered by our solutions.…”