[1][2][3] Process-tracing can be defined as the following: it is the systematic examination of diagnostic evidence selected and analyzed in light of research questions and hypotheses posed by the investigator (Collier, 2011).
It is generally understood as a "within-case" method to draw inferences on the basis of causal mechanisms, but it can also be used for ideographic research or small-N case-studies.
[5][6] By using Bayesian probability, it may be possible to make strong causal inferences from a small sliver of data through process tracing.
[9] In 'theory-testing process tracing,' the goal is to test existing theories and the causal mechanisms assumed therein.
[9][10] On the contrary, 'theory-building process tracing' involves constructing a theory about a causal mechanism that can be applied to a broader population of a particular phenomenon.
[9] This variant constructs a detailed narrative that explains the process through which a specific outcome or series of events came to be.
[16][17] While some influential works by methods scholars have argued that the ability of process-tracing to make causal claims is limited by low degrees of freedom,[18] methodologists widely reject that the "degrees of freedom" problem applies to research that uses process-tracing, given that qualitative research entails different logics than quantitative research (where scholars do need to be wary of degrees of freedom).
[1] In addition to aiding uncovering and testing causal mechanisms, process-tracing also contributes descriptive richness.
[19] Another important advantage is that process tracing can deal with theoretical pluralism, which means hypotheses or conceptual models have multiple (un)dependent variables and causal relationships.