Process tracing is a theory-based method for evaluating what contributed to program or policy outcomes in the cases studied. Process-tracing methods are particularly useful for evaluating how intangible interventions, such as knowledge work and institution building, have contributed to outcomes. Process tracing can be deployed either as a stand-alone method for evaluating a policy or program or as part of a broader evaluation in which it is used to examine in detail the processes that produced particular contributions to a policy or program’s outcomes.

As an evaluation method, process tracing has three components: (i) a “process” theory, which is a granular causal theory that links an intervention and contribution through a process theory of change (pToC) that models, theoretically, the sequence of interactions between a particular policy or program intervention and a particular contribution to a policy or program outcome; (ii) “tracing” of the pToC by assessing empirical observables produced by the activities and links in the process; and (iii) drawing of more general lessons from the cases studied by identifying why the intervention worked in those cases and what contextual factors need to be present for it to work in analogous ways in other cases.

Process tracing is in the family of theory-based evaluation methods, together with contribution analysis and realist evaluation (Lemire et al. 2020). It has comparative strengths in theorizing and providing evidence for more granular theoretical processes that link policy or program interventions with contributions to policy or program outcomes (Aston et al. 2022; Schmitt and Beach 2015; Wauters and Beach 2018). Practitioners of process tracing develop theories and gather evidence in support of them through a continued dialogue between the empirical record of a case they are studying and a preliminary pToC, which they revise and update as they collect new evidence during the evaluation. Process tracing, therefore, helps evaluators understand how interventions have actually worked in real-world cases (Raimondo and Beach 2024).

Process tracing offers a language that enables evaluators to develop more granular, step-by-step theorizations regarding how particular interventions produce contributions to policy or program outcomes. Evaluators accomplish this by outlining, in a pToC, the interactions between the actors involved in an intervention and the actors affected by those interventions (Camacho and Beach 2023; Cartwright 2021). Working with more granular theories of change (ToCs) regarding the processes that link interventions and contributions offers three main analytical benefits for evaluations. First, evaluators can make more credible evidence-based claims about contributions (Schmitt 2020). Detailing the chain of activities and links in an intervention in theoretical terms makes it easier for evaluators to develop testable hypotheses about the empirical observables that might be left if the pToC worked as theorized. Developing explicit, testable expectations about empirical observables provides focus for empirical fieldwork because the task becomes assessing whether the expected empirics were actually present in the case or not. If the expected observables are not found, the pToC should be revised to account for how it actually worked (or did not work). Second, an empirically validated pToC sheds more light on how a particular intervention produced a specific contribution, thereby providing actionable knowledge that can both help improve implementation of the intervention in the case studied (if ongoing) and inspire design and implementation in other programs (Schmitt 2020; Sridharan and Nakaima 2012). Third, by focusing on the concrete activities of key actors during key causal episodes, process tracing helps generate practical lessons about how interventions work and how they can work better in real-world contexts (Raimondo 2020).

The rest of this paper explains how process tracing works in practice. We provide a step-by-step guide to using process tracing through an examination of a recent application of the method in an Independent Evaluation Group (IEG) evaluation. The evaluation used process tracing as part of a broader evaluation of the World Bank Group’s engagement in a middle-income country. The process tracing focused on whether the World Bank’s data and diagnostic work in the client country, in a context of national sensitivity to outside intervention, had a positive impact on the country’s policy coherence. Given the sensitive nature of the questions involved in the evaluation, we present an anonymized version of the process-tracing case study. Using process tracing, the evaluation examined the World Bank’s convening and policy dialogue activities, including those with a think tank engaged by the client country, surrounding the production and dissemination of a major diagnostic report over four years. The evaluation also looked at the report’s policy consequences several years after its publication. Although the World Bank’s impact in middle-income countries comes as much from data, analytics, and advisory services as it does from the financing it provides, impacts from the former tend to be understudied and underevaluated, in part because of the lack of awareness of, and use of, process tracing and other methods. The IEG report was thus used as a proof of concept of the potential for process tracing to fill this knowledge gap.

The paper proceeds as follows: Chapter 1 provides guidance on how to construct a granular pToC. Chapter 2 lays out how this pToC, once constructed, can be traced empirically. Chapter 3 identifies ways of drawing lessons from process-tracing case studies that can be applied to cases other than the one studied. Chapter 4 concludes with reflections on the applicability and limitations of process tracing.