Publications of Rohlfing, I.

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

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 set-relational causation in terms of necessity and sufficiency has important consequences for the choice of cases. Using real world data for both crisp-set and fuzzy-set QCA, we show what typical and deviant cases are in QCA-based 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.

Does set-relational causation fit into a potential outcomes framework? An Assessment of Gerring’s Proposal

One of John Gerring’s aims in his intriguing treatment of social science methodology is the development of a unified account for causal inference on the basis of the potential outcomes (PO) framework (Gerring, John (2012): Social Science Methodology: A Unified Framework. Cambridge: Cambridge University Press.). Over the past two decades, the PO framework has become central in quantitative analyses. In qualitative research, in contrast, set theory and set-relational (SR) forms of causation and empirical research have started to play an ever more important role. According to Gerring, the PO account is the more general framework and is able to accommodate SR causation such as necessity and sufficiency. In our contribution to this symposium, we discuss the viability of Gerring’s proposal on how to perform SR research on the basis of the PO framework. Most importantly, we show that the suggested procedure can produce false negatives – indicating the absence of a set relation when, in fact, one exists – and false positives – suggesting the presence of a set relation when there is none. In the concluding section, we detail that if the PO and SR frameworks are truly compatible, all of these SR features must be transposed into the PO framework.