Comparative case studies are undertaken over time and emphasize comparison within and across contexts. Comparative case studies may be selected when it is not feasible to undertake an experimental design and when there is a need to understand and explain how features within the context influence the success of program or policy initiatives (Goodrick, 2014).
Comparative case studies involve the analysis and synthesis of the similarities, differences, and patterns across two or more cases that share a common focus or goal. Comparative case studies often incorporate both qualitative and quantitative data. Given the focus on generating a good understanding of the cases and case context, methods such as fieldwork visits, observation, interviews and document analysis often dominate among the various data collection methods employed (Goodrick, 2014).
Case study methods have considerable comparative advantages relative to statistical methods or formal models (Goodrick, 2014). These include the operationalization and measurement of qualitative variables (construct validity), the heuristic identi‹cation of new variables or hypotheses, the examination of potential causal mechanisms within particular cases or contexts, the historical explanation of cases, and the incorporation of complex relations like equality and path dependency into typological theories
Comparative case studies require a range of skills and expertise. As with other designs it is important to assess the match between the required skill set and the evaluation team. Comparative case studies have disadvantages in some contexts (Goodrick, 2014). One key issue is that they are often highly resource-intensive, particularly if extensive fieldwork is required. Comparative case studies can be based entirely on secondary data analysis, and thus require no fieldwork or primary data collection at all. The quality of available evidence must be suitably strong for this to be an appropriate option, however. Findings can be less reliable if there is too much of a time lag between cases in the comparison activity.
Single-Case Research Designs
Single case design (SCD), often referred to as single-subject design, is an evaluation method that can be used to rigorously test the success of an intervention or treatment on a particular case (i.e., a person, school, community) and to also provide evidence about the general effectiveness of an intervention using a relatively small sample size. SCDs use visual analysis of data to systematically compare participants’ target behaviors before they receive an intervention to the same behaviors during and after the intervention has been introduced (Willis, 2014). If the data illustrate that target behaviors change only after the intervention is initiated, this effect suggests that the intervention was responsible for the behavior change. To establish causal evidence that the intervention was, in fact, responsible for behavior change, replication of the effect is then attempted.
An advantage of using an SSRD is that, instead of comparing the percentage of people that responded to an experimental factor to the percentage of people that did not, the study examines how an individual subject, with his unique characteristics, responds to the experimental factor (Willis, 2014). An SSRD allows researchers to quickly design and run their study without having to find so many participants.
While the fact that the researcher does not use a large number of participants has its advantages, it also has a downside: Because the experimental trials are run on only one subject, it is difficult to empirically show with the experiment’s data that the findings will generalize out to larger populations. All the trial can show is what happened with the individual subject, whereas traditional research designs that use large numbers of participants are specifically designed to show if a result is statistically valid for the general population (Willis, 2014).
Counterfactual impact evaluation
In its simplest form, counterfactual impact evaluation (CIE) is a method of comparison which involves comparing the outcomes of interest of those having benefitted from a policy or programme (the “treated group”) with those of a group similar in all respects to the treatment group (the “comparison/control group”), the only difference being that the comparison/control group has not been exposed to the policy or programme. The comparison group provides information on “what would have happened to the members subject to the intervention had they not been exposed to it,” the counterfactual case (Levy, 2015).
The case for counterfactual impact evaluation is based on the need to collect evidence and determine whether policy objectives have been met and, ultimately, whether the resources were used efficiently. These answers feed back into the design and implementation of future interventions and budgetary decisions. In light of this, the European Commission is committed to making impact evaluation part of a policy implementation life-cycle (Levy, 2015).
The single case study is the preferred choice as a researcher. The various forms of single case study analysis can – through the application of multiple qualitative and quantitative research methods – provide a nuanced, empirically-rich, holistic account of specific phenomena. This may be particularly appropriate for those phenomena that are simply less amenable to more superficial measures and tests (or indeed any substantive form of quantification) as well as those for which our reasons for understanding and/or explaining them are irreducibly subjective – as, for example, with many of the normative and ethical issues associated with the practice of international relations (Gustafsson, 2017). From various epistemological and analytical standpoints, single case study analysis can incorporate both idiographic sui generis cases and, where the potential for generalization may exist, nomothetic case studies suitable for the testing and building of causal hypotheses. Finally, it should not be ignored that a signal advantage of the case study – with particular relevance to international relations – also exists at a more practical rather than theoretical level (Gustafsson, 2017).
Goodrick, D. (2014). Comparative Case Studies: Methodological Briefs-Impact Evaluation No. 9 (No. innpub754).
Gustafsson, J. (2017). Single case studies vs. multiple case studies: A comparative study.
Levy, J. S. (2015). Counterfactuals, causal inference, and historical analysis. Security Studies, 24(3), 378-402.
Willis, B. (2014). The advantages and limitations of single case study analysis. E-International Relations.