Compare methods

	Most Similar Systems Design	Process Tracing
Field	Political Science	Psychometrics
Family	Process / pipeline	Latent structure
Year of origin	1970	2005
Originator	John Stuart Mill (method of difference); Przeworski & Teune (systems framing)	Alexander George, Andrew Bennett
Type	Small-N comparative case-selection design	Qualitative causal inference
Seminal source	Przeworski, A., & Teune, H. (1970). The Logic of Comparative Social Inquiry. New York: Wiley-Interscience. ISBN: 9780471701422	Bennett, A., & Checkel, J. T. (Eds.). (2015). Process Tracing: From Metaphor to Analytic Tool. Cambridge University Press.
Aliases	MSSD, Most similar cases design, Mill's method of difference, Comparable cases strategy	—
Related	3	5
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.	Process Tracing is a qualitative research method developed by George and Bennett (2005) for studying causal mechanisms and causal chains within individual cases. It involves examining the sequence of events and decision-making processes within a case to infer whether a hypothesized causal mechanism actually operated. Process tracing aims to strengthen causal inference in case studies by looking beyond correlation to understand how causes produce effects.