Compare methods

	Most Similar Systems Design	Most Different Systems Design
Field	Political Science	Political Science
Family	Process / pipeline	Process / pipeline
Year of origin	1970	1970
Originator	John Stuart Mill (method of difference); Przeworski & Teune (systems framing)	John Stuart Mill (method of agreement); Przeworski & Teune (systems framing)
Type	Small-N comparative case-selection design	Small-N comparative case-selection design
Seminal source	Przeworski, A., & Teune, H. (1970). The Logic of Comparative Social Inquiry. New York: Wiley-Interscience. ISBN: 9780471701422	Przeworski, A., & Teune, H. (1970). The Logic of Comparative Social Inquiry. New York: Wiley-Interscience. ISBN: 9780471701422
Aliases	MSSD, Most similar cases design, Mill's method of difference, Comparable cases strategy	MDSD, Most different cases design, Mill's method of agreement, Diverse systems design
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.	The most different systems design (MDSD) is a small-N comparative strategy that selects cases that differ on as many background characteristics as possible yet share the same outcome. If wildly dissimilar cases nonetheless converge on the same result, the explanation cannot lie in the many features on which they differ — it must lie in whatever they have in common. Grounded in John Stuart Mill's method of agreement and named by Przeworski and Teune, it is the mirror image of the most similar systems design and a staple of comparative politics.