Compare methods

	Most Similar Systems Design	Qualitative Comparative Analysis
Field	Political Science	Political Science
Family	Process / pipeline	Process / pipeline
Year of origin	1970	1987
Originator	John Stuart Mill (method of difference); Przeworski & Teune (systems framing)	Charles C. Ragin
Type	Small-N comparative case-selection design	Set-theoretic, configurational comparative method
Seminal source	Przeworski, A., & Teune, H. (1970). The Logic of Comparative Social Inquiry. New York: Wiley-Interscience. ISBN: 9780471701422	Ragin, C. C. (1987). The Comparative Method: Moving Beyond Qualitative and Quantitative Strategies. Berkeley: University of California Press. ISBN: 9780520058347
Aliases	MSSD, Most similar cases design, Mill's method of difference, Comparable cases strategy	QCA, csQCA, fsQCA, Configurational comparative method
Related	3	3
Summary	The most similar systems design (MSSD) is a small-N comparative strategy that selects cases as alike as possible on many background characteristics but differing on the outcome of interest. By matching cases so that most potential confounders are held roughly constant, the design isolates the few factors that vary alongside the outcome as the candidate causes. Rooted in John Stuart Mill's method of difference and named by Przeworski and Teune, it is a cornerstone of comparative politics for drawing causal inferences from a handful of countries or cases.	Qualitative Comparative Analysis (QCA) is a set-theoretic, configurational method that identifies which combinations of conditions are necessary or sufficient for an outcome across a set of cases. Developed by Charles Ragin, it treats each case as a configuration of set memberships, builds a truth table of all logically possible combinations, and uses Boolean algebra to minimize them into the simplest expressions that account for the outcome. It bridges qualitative case knowledge and cross-case generalization, embracing causal complexity through conjunctural causation, equifinality, and asymmetry.