Process Tracing

Process tracing is a case-based approach to causal inference which focuses on the use of clues within a case (causal-process observations, CPOs) to adjudicate between alternative possible explanations. 

Process tracing involves four types of causal tests -

  • 'straw in the wind', which lends support for an explanation without definitively ruling it in or out,
  • 'hoop', failed when examination of a case shows the presence of a necessary causal condition,when the outcome of interest is not present. Common hoop conditions are more persuasive than uncommon ones
  • 'smoking gun', passed when examination of a case shows the presence of a sufficient causal condition. Uncommon smoking gun conditions are more persuasive than common ones
  • 'doubly definitive' passed when examination of a case shows that a condition is both necessary and sufficient support for the explanation. These tend to be rare.

Process tracing can be used both to see if results are consistent with the program theory (theory of change) and to see if alternative explanations can be ruled out.


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Guides and Examples

  • Understanding Process Tracing: This article provides examples and a comprehensive framework for the use of Process Tracing. It is accompanied by online teaching exercises and  a series of focused examples.
  • Process Tracing: Introduction and Exercises: This document provides an overview of the method of process tracing and a series of examples and exercises to aid in its teaching .
Updated: 1st May 2014 - 5:10am
A special thanks to this page's contributors
Monitoring and Evaluation Consultant, MandE NEWS.
United Kingdom.
Research Assistant, RMIT University.
Professor of Public Sector Evaluation, RMIT University.


rickjdavies's picture
rick davies

Mahoney, James. 2012. “Mahoney, J. (2012). The Logic of Process Tracing Tests in the Social Sciences. 1-28.” Sociological Methods & Research XX(X) (March 2): 1–28. doi:10.1177/0049124112437709.

This article discusses process tracing as a methodology for testing hypoth-eses in the social sciences. With process tracing tests, the analyst combines preexisting generalizations with specific observations from within a single case to make causal inferences about that case. Process tracing tests can be used to help establish that (1) an initial event or process took place, (2) a subsequent outcome also occurred, and (3) the former was a cause of the latter. The article focuses on the logic of different process tracing tests,including hoop tests, smoking gun tests, and straw in the wind tests. New criteria for judging the strength of these tests are developed using ideas concerning the relative importance of necessary and sufficient conditions. Similarities and differences between process tracing and the deductivenomological model of explanation are explored.

Anonymous's picture
Ingo Rohlfing

Fairfield applies the typology, though I am not sure she understands the tests in the same way as they are described above. (Fairfield, Tasha (2013): Going Where the Money Is: Strategies for Taxing Economic Elites in Unequal Democracies. World Development 47: 42-57.)

I might add that I have written an article in which I show that the understanding of the doubly decisive test is misleading and that it lumps together the criteria of uniqueness and contradiction. (Rohlfing, Ingo (2014): Comparative Hypothesis Testing Via Process Tracing. Sociological Methods & Research 43 (4): 606-642.)

I also think the above description is too narrow. There is no reason to narrow the tests to necessary and sufficient conditions because they express a logic of testing that is widely applicable (also beyond process tracing). The misunderstanding might come from Bennett's 2010 book section (Bennett, Andrew (2010): Process Tracing and Causal Inference. Brady, Henry E. and David Collier (ed.):  Rethinking Social Inquiry: Diverse Tools, Shared Standards.  Lanham: Rowman & Littlefield: 207-219), picked up by Colier (Collier, David (2011): Understanding Process Tracing. PS: Political Science & Politics 44 (4): 823-830). They invoke necessary and sufficient test criteria which are different from necessary and sufficient conditions. Finally, Bennett argues in his contribution to vol. 12, issue 1 of the newsleter of the APSA Section on Qualitative and Multi-Method Research that Bayesianism outperforms the four types of tests because it is more flexible.

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