Single-Case Designs

Conceptual Overview and Discussion

Single-case designs are commonly used approaches to the planning of a case study inquiry. In analogy to a single experiment, Robert Yin describes a series of circumstances under which a single-case design can be appropriately employed to achieve the goal of a case study research. Notably, a critical case can be utilized to confirm, challenge, or extend an existing theory through testing related propositions or suggesting alternative explanations. An extreme case makes a good instance for the documentation and analysis of an event because of its uniqueness or rarity in occurrences. Representative cases are often used as a caricature of an event or entity that typically reoccurs and thus these are used to show how lessons from one case can be applied to (generalized) to the next. The opportunity or privilege of gaining access to a site or phenomenon that is otherwise inaccessible to researchers justifies the use of a revelatory case on the grounds of uncovering issues of common concerns, whereas investigating a phenomenon at different points in time calls for a longitudinal case to elucidate changes or analyze trends over time.

Defining a case and its units of analysis is a major step or component in developing a single-case design. Depending on the units (or levels) of analysis to be implemented in the research, a single-case study can either follow a holistic or an embedded design. Very often, a case can be an individual, as in the instance of life histories, in which a study's subject forms a holistic unit of the analysis. It can also be an association with lower level constituents, such as chapters and members, which may involve multiple units of analysis as in an embedded design. In the design process, [Page 868]defining units of analysis comes after, or as a result of, the objectives and questions of a case study. In general terms, the formulation of research questions and study propositions should lead to the selection of appropriate unit or units of analysis.

Yin discusses the use of validity and reliability as conditions or criteria to watch for in order to maximize design quality in single-case studies. He notes theory development as an essential part of such a design regardless of whether an ensuing case study's purpose is to develop or test theory. In view of a typical criticism that the external validity of single-case designs is an inadequate basis for drawing conclusions, Yin states that in such designs the notion of generalization is meant to analytically generalize a particular set of results to broader theories, in which reliability is taken as the repetition of the same case study by another investigator or at another time, rather than intended as a replication of one case design to another case.

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